[SCSI] dc395x: dynamically map scatter-gather for PIO

The current dc395x driver uses PIO to transfer up to 4 bytes which do not
get transferred by DMA (under unclear circumstances). For this the driver
uses page_address() which is broken on highmem. Apart from this the
actual calculation of the virtual address is wrong (even without highmem).
So, e.g., for reading it reads bytes from the driver to a wrong address
and returns wrong data, I guess, for writing it would just output random
data to the device.

The proper fix, as suggested by many, is to dynamically map data using
kmap_atomic(page, KM_BIO_SRC_IRQ) / kunmap_atomic(virt). The reason why it
has not been done until now, although I've done some preliminary patches
more than a year ago was that nobody interested in fixing this problem was
able to reliably reproduce it. Now it changed - with the help from
Sebastian Frei (CC'ed) I was able to trigger the PIO path. Thus, I was
also able to test and debug it.

There are 4 cases when PIO is used in dc395x - data-in / -out with and
without scatter-gather. I was able to reproduce and test only data-in with
and without SG. So, the data-out path is still untested, but it is also
somewhat simpler than the data-in. Fredrik Roubert (also CC'ed) also had
PIO triggering on his system, and in his case it was data-out without SG.
It would be great if he could test the attached patch on his system, but
even if he cannot, I would still request to apply the patch and just wait
if anybody cries...

Implementation: I put 2 new functions in scsi_lib.c and their declarations
in scsi_cmnd.h. I exported them without _GPL, although, I don't feel
strongly about that - not many drivers are likely to use them. But there
is at least one more - I want to use them in tmscsim.c. Whether these are
the right files for the functions and their declarations - not sure
either. Actually, they are not scsi-specific, so, might go somewhere
around other scattergather magic? They are not platform specific either,
and most SG functions are defined under arch/*/... As these issues were
discussed previously there were some more routines suggested to manipulate
scattergather buffers, I think, some of them were needed around
crypto code... So, might be a common place reasonable, like
lib/scattergather.c? I am open here.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/dc395x.c

@@ -230,13 +230,12 @@ struct ScsiReqBlk {
 	struct scsi_cmnd *cmd;
 
 	struct SGentry *segment_x;	/* Linear array of hw sg entries (up to 64 entries) */
-	u32 sg_bus_addr;	        /* Bus address of sg list (ie, of segment_x) */
+	dma_addr_t sg_bus_addr;	        /* Bus address of sg list (ie, of segment_x) */
 
 	u8 sg_count;			/* No of HW sg entries for this request */
 	u8 sg_index;			/* Index of HW sg entry for this request */
-	u32 total_xfer_length;		/* Total number of bytes remaining to be transfered */
-	unsigned char *virt_addr;	/* Virtual address of current transfer position */
-
+	size_t total_xfer_length;	/* Total number of bytes remaining to be transfered */
+	size_t request_length;		/* Total number of bytes in this request */
 	/*
 	 * The sense buffer handling function, request_sense, uses
 	 * the first hw sg entry (segment_x[0]) and the transfer
@@ -246,8 +245,7 @@ struct ScsiReqBlk {
 	 * total_xfer_length in xferred. These values are restored in
 	 * pci_unmap_srb_sense. This is the only place xferred is used.
 	 */
-	unsigned char *virt_addr_req;	/* Saved virtual address of the request buffer */
-	u32 xferred;		        /* Saved copy of total_xfer_length */
+	size_t xferred;		        /* Saved copy of total_xfer_length */
 
 	u16 state;
 
@@ -977,17 +975,6 @@ static void send_srb(struct AdapterCtlBlk *acb, struct ScsiReqBlk *srb)
 	}
 }
 
-static inline void pio_trigger(void)
-{
-	static int feedback_requested;
-
-	if (!feedback_requested) {
-		feedback_requested = 1;
-		printk(KERN_WARNING "%s: Please, contact <linux-scsi@vger.kernel.org> "
-		       "to help improve support for your system.\n", __FILE__);
-	}
-}
-
 /* Prepare SRB for being sent to Device DCB w/ command *cmd */
 static void build_srb(struct scsi_cmnd *cmd, struct DeviceCtlBlk *dcb,
 		struct ScsiReqBlk *srb)
@@ -1001,7 +988,6 @@ static void build_srb(struct scsi_cmnd *cmd, struct DeviceCtlBlk *dcb,
 	srb->sg_count = 0;
 	srb->total_xfer_length = 0;
 	srb->sg_bus_addr = 0;
-	srb->virt_addr = NULL;
 	srb->sg_index = 0;
 	srb->adapter_status = 0;
 	srb->target_status = 0;
@@ -1032,7 +1018,6 @@ static void build_srb(struct scsi_cmnd *cmd, struct DeviceCtlBlk *dcb,
 			reqlen, cmd->request_buffer, cmd->use_sg,
 			srb->sg_count);
 
-		srb->virt_addr = page_address(sl->page);
 		for (i = 0; i < srb->sg_count; i++) {
 			u32 busaddr = (u32)sg_dma_address(&sl[i]);
 			u32 seglen = (u32)sl[i].length;
@@ -1077,12 +1062,14 @@ static void build_srb(struct scsi_cmnd *cmd, struct DeviceCtlBlk *dcb,
 			srb->total_xfer_length++;
 
 		srb->segment_x[0].length = srb->total_xfer_length;
-		srb->virt_addr = cmd->request_buffer;
+
 		dprintkdbg(DBG_0,
 			"build_srb: [1] len=%d buf=%p use_sg=%d map=%08x\n",
 			srb->total_xfer_length, cmd->request_buffer,
 			cmd->use_sg, srb->segment_x[0].address);
 	}
+
+	srb->request_length = srb->total_xfer_length;
 }
 
 
@@ -1414,10 +1401,10 @@ static int dc395x_eh_abort(struct scsi_cmnd *cmd)
 	}
 	srb = find_cmd(cmd, &dcb->srb_going_list);
 	if (srb) {
-		dprintkl(KERN_DEBUG, "eh_abort: Command in progress");
+		dprintkl(KERN_DEBUG, "eh_abort: Command in progress\n");
 		/* XXX: Should abort the command here */
 	} else {
-		dprintkl(KERN_DEBUG, "eh_abort: Command not found");
+		dprintkl(KERN_DEBUG, "eh_abort: Command not found\n");
 	}
 	return FAILED;
 }
@@ -1976,14 +1963,11 @@ static void sg_verify_length(struct ScsiReqBlk *srb)
 
 /*
  * Compute the next Scatter Gather list index and adjust its length
- * and address if necessary; also compute virt_addr
+ * and address if necessary
  */
 static void sg_update_list(struct ScsiReqBlk *srb, u32 left)
 {
 	u8 idx;
-	struct scatterlist *sg;
-	struct scsi_cmnd *cmd = srb->cmd;
-	int segment = cmd->use_sg;
 	u32 xferred = srb->total_xfer_length - left; /* bytes transfered */
 	struct SGentry *psge = srb->segment_x + srb->sg_index;
 
@@ -2016,29 +2000,6 @@ static void sg_update_list(struct ScsiReqBlk *srb, u32 left)
 		psge++;
 	}
 	sg_verify_length(srb);
-
-	/* we need the corresponding virtual address */
-	if (!segment || (srb->flag & AUTO_REQSENSE)) {
-		srb->virt_addr += xferred;
-		return;
-	}
-
-	/* We have to walk the scatterlist to find it */
-	sg = (struct scatterlist *)cmd->request_buffer;
-	while (segment--) {
-		unsigned long mask =
-		    ~((unsigned long)sg->length - 1) & PAGE_MASK;
-		if ((sg_dma_address(sg) & mask) == (psge->address & mask)) {
-			srb->virt_addr = (page_address(sg->page)
-					   + psge->address -
-					   (psge->address & PAGE_MASK));
-			return;
-		}
-		++sg;
-	}
-
-	dprintkl(KERN_ERR, "sg_update_list: sg_to_virt failed\n");
-	srb->virt_addr = NULL;
 }
 
 
@@ -2050,15 +2011,7 @@ static void sg_update_list(struct ScsiReqBlk *srb, u32 left)
  */
 static void sg_subtract_one(struct ScsiReqBlk *srb)
 {
-	srb->total_xfer_length--;
-	srb->segment_x[srb->sg_index].length--;
-	if (srb->total_xfer_length &&
-	    !srb->segment_x[srb->sg_index].length) {
-		if (debug_enabled(DBG_PIO))
-			printk(" (next segment)");
-		srb->sg_index++;
-		sg_update_list(srb, srb->total_xfer_length);
-	}
+	sg_update_list(srb, srb->total_xfer_length - 1);
 }
 
 
@@ -2118,7 +2071,7 @@ static void data_out_phase0(struct AdapterCtlBlk *acb, struct ScsiReqBlk *srb,
 	 * If we need more data, the DMA SG list will be freshly set up, anyway
 	 */
 	dprintkdbg(DBG_PIO, "data_out_phase0: "
-		"DMA{fifcnt=0x%02x fifostat=0x%02x} "
+		"DMA{fifocnt=0x%02x fifostat=0x%02x} "
 		"SCSI{fifocnt=0x%02x cnt=0x%06x status=0x%04x} total=0x%06x\n",
 		DC395x_read8(acb, TRM_S1040_DMA_FIFOCNT),
 		DC395x_read8(acb, TRM_S1040_DMA_FIFOSTAT),
@@ -2239,12 +2192,11 @@ static void data_out_phase1(struct AdapterCtlBlk *acb, struct ScsiReqBlk *srb,
 	data_io_transfer(acb, srb, XFERDATAOUT);
 }
 
-
 static void data_in_phase0(struct AdapterCtlBlk *acb, struct ScsiReqBlk *srb,
 		u16 *pscsi_status)
 {
 	u16 scsi_status = *pscsi_status;
-	u32 d_left_counter = 0;
+
 	dprintkdbg(DBG_0, "data_in_phase0: (pid#%li) <%02i-%i>\n",
 		srb->cmd->pid, srb->cmd->device->id, srb->cmd->device->lun);
 
@@ -2262,6 +2214,9 @@ static void data_in_phase0(struct AdapterCtlBlk *acb, struct ScsiReqBlk *srb,
 	 * seem to be a bad idea, actually.
 	 */
 	if (!(srb->state & SRB_XFERPAD)) {
+		u32 d_left_counter;
+		unsigned int sc, fc;
+
 		if (scsi_status & PARITYERROR) {
 			dprintkl(KERN_INFO, "data_in_phase0: (pid#%li) "
 				"Parity Error\n", srb->cmd->pid);
@@ -2298,18 +2253,19 @@ static void data_in_phase0(struct AdapterCtlBlk *acb, struct ScsiReqBlk *srb,
 				DC395x_read8(acb, TRM_S1040_DMA_FIFOSTAT));
 		}
 		/* Now: Check remainig data: The SCSI counters should tell us ... */
-		d_left_counter = DC395x_read32(acb, TRM_S1040_SCSI_COUNTER)
-		    + ((DC395x_read8(acb, TRM_S1040_SCSI_FIFOCNT) & 0x1f)
+		sc = DC395x_read32(acb, TRM_S1040_SCSI_COUNTER);
+		fc = DC395x_read8(acb, TRM_S1040_SCSI_FIFOCNT);
+		d_left_counter = sc + ((fc & 0x1f)
 		       << ((srb->dcb->sync_period & WIDE_SYNC) ? 1 :
 			   0));
 		dprintkdbg(DBG_KG, "data_in_phase0: "
 			"SCSI{fifocnt=0x%02x%s ctr=0x%08x} "
 			"DMA{fifocnt=0x%02x fifostat=0x%02x ctr=0x%08x} "
 			"Remain{totxfer=%i scsi_fifo+ctr=%i}\n",
-			DC395x_read8(acb, TRM_S1040_SCSI_FIFOCNT),
+			fc,
 			(srb->dcb->sync_period & WIDE_SYNC) ? "words" : "bytes",
-			DC395x_read32(acb, TRM_S1040_SCSI_COUNTER),
-			DC395x_read8(acb, TRM_S1040_DMA_FIFOCNT),
+			sc,
+			fc,
 			DC395x_read8(acb, TRM_S1040_DMA_FIFOSTAT),
 			DC395x_read32(acb, TRM_S1040_DMA_CXCNT),
 			srb->total_xfer_length, d_left_counter);
@@ -2317,40 +2273,79 @@ static void data_in_phase0(struct AdapterCtlBlk *acb, struct ScsiReqBlk *srb,
 		/* KG: Less than or equal to 4 bytes can not be transfered via DMA, it seems. */
 		if (d_left_counter
 		    && srb->total_xfer_length <= DC395x_LASTPIO) {
+			size_t left_io = srb->total_xfer_length;
+
 			/*u32 addr = (srb->segment_x[srb->sg_index].address); */
 			/*sg_update_list (srb, d_left_counter); */
-			dprintkdbg(DBG_PIO, "data_in_phase0: PIO (%i %s) to "
-				"%p for remaining %i bytes:",
-				DC395x_read8(acb, TRM_S1040_SCSI_FIFOCNT) & 0x1f,
+			dprintkdbg(DBG_PIO, "data_in_phase0: PIO (%i %s) "
+				   "for remaining %i bytes:",
+				fc & 0x1f,
 				(srb->dcb->sync_period & WIDE_SYNC) ?
 				    "words" : "bytes",
-				srb->virt_addr,
 				srb->total_xfer_length);
 			if (srb->dcb->sync_period & WIDE_SYNC)
 				DC395x_write8(acb, TRM_S1040_SCSI_CONFIG2,
 					      CFG2_WIDEFIFO);
-			while (DC395x_read8(acb, TRM_S1040_SCSI_FIFOCNT) != 0x40) {
-				u8 byte = DC395x_read8(acb, TRM_S1040_SCSI_FIFO);
-				pio_trigger();
-				*(srb->virt_addr)++ = byte;
-				if (debug_enabled(DBG_PIO))
-					printk(" %02x", byte);
-				d_left_counter--;
-				sg_subtract_one(srb);
-			}
-			if (srb->dcb->sync_period & WIDE_SYNC) {
-#if 1
-                /* Read the last byte ... */
-				if (srb->total_xfer_length > 0) {
-					u8 byte = DC395x_read8(acb, TRM_S1040_SCSI_FIFO);
-					pio_trigger();
-					*(srb->virt_addr)++ = byte;
-					srb->total_xfer_length--;
+			while (left_io) {
+				unsigned char *virt, *base = NULL;
+				unsigned long flags = 0;
+				size_t len = left_io;
+
+				if (srb->cmd->use_sg) {
+					size_t offset = srb->request_length - left_io;
+					local_irq_save(flags);
+					/* Assumption: it's inside one page as it's at most 4 bytes and
+					   I just assume it's on a 4-byte boundary */
+					base = scsi_kmap_atomic_sg((struct scatterlist *)srb->cmd->request_buffer,
+								     srb->sg_count, &offset, &len);
+					virt = base + offset;
+				} else {
+					virt = srb->cmd->request_buffer + srb->cmd->request_bufflen - left_io;
+					len = left_io;
+				}
+				left_io -= len;
+
+				while (len) {
+					u8 byte;
+					byte = DC395x_read8(acb, TRM_S1040_SCSI_FIFO);
+					*virt++ = byte;
+
 					if (debug_enabled(DBG_PIO))
 						printk(" %02x", byte);
+
+					d_left_counter--;
+					sg_subtract_one(srb);
+
+					len--;
+
+					fc = DC395x_read8(acb, TRM_S1040_SCSI_FIFOCNT);
+
+					if (fc == 0x40) {
+						left_io = 0;
+						break;
+					}
+				}
+
+				WARN_ON((fc != 0x40) == !d_left_counter);
+
+				if (fc == 0x40 && (srb->dcb->sync_period & WIDE_SYNC)) {
+					/* Read the last byte ... */
+					if (srb->total_xfer_length > 0) {
+						u8 byte = DC395x_read8(acb, TRM_S1040_SCSI_FIFO);
+
+						*virt++ = byte;
+						srb->total_xfer_length--;
+						if (debug_enabled(DBG_PIO))
+							printk(" %02x", byte);
+					}
+
+					DC395x_write8(acb, TRM_S1040_SCSI_CONFIG2, 0);
+				}
+
+				if (srb->cmd->use_sg) {
+					scsi_kunmap_atomic_sg(base);
+					local_irq_restore(flags);
 				}
-#endif
-				DC395x_write8(acb, TRM_S1040_SCSI_CONFIG2, 0);
 			}
 			/*printk(" %08x", *(u32*)(bus_to_virt (addr))); */
 			/*srb->total_xfer_length = 0; */
@@ -2509,22 +2504,43 @@ static void data_io_transfer(struct AdapterCtlBlk *acb,
 				      SCMD_FIFO_IN);
 		} else {	/* write */
 			int ln = srb->total_xfer_length;
+			size_t left_io = srb->total_xfer_length;
+
 			if (srb->dcb->sync_period & WIDE_SYNC)
 				DC395x_write8(acb, TRM_S1040_SCSI_CONFIG2,
 				     CFG2_WIDEFIFO);
-			dprintkdbg(DBG_PIO,
-				"data_io_transfer: PIO %i bytes from %p:",
-				srb->total_xfer_length, srb->virt_addr);
 
-			while (srb->total_xfer_length) {
-				if (debug_enabled(DBG_PIO))
-					printk(" %02x", (unsigned char) *(srb->virt_addr));
+			while (left_io) {
+				unsigned char *virt, *base = NULL;
+				unsigned long flags = 0;
+				size_t len = left_io;
+
+				if (srb->cmd->use_sg) {
+					size_t offset = srb->request_length - left_io;
+					local_irq_save(flags);
+					/* Again, max 4 bytes */
+					base = scsi_kmap_atomic_sg((struct scatterlist *)srb->cmd->request_buffer,
+								     srb->sg_count, &offset, &len);
+					virt = base + offset;
+				} else {
+					virt = srb->cmd->request_buffer + srb->cmd->request_bufflen - left_io;
+					len = left_io;
+				}
+				left_io -= len;
+
+				while (len--) {
+					if (debug_enabled(DBG_PIO))
+						printk(" %02x", *virt);
 
-				pio_trigger();
-				DC395x_write8(acb, TRM_S1040_SCSI_FIFO, 
-				     *(srb->virt_addr)++);
+					DC395x_write8(acb, TRM_S1040_SCSI_FIFO, *virt++);
 
-				sg_subtract_one(srb);
+					sg_subtract_one(srb);
+				}
+
+				if (srb->cmd->use_sg) {
+					scsi_kunmap_atomic_sg(base);
+					local_irq_restore(flags);
+				}
 			}
 			if (srb->dcb->sync_period & WIDE_SYNC) {
 				if (ln % 2) {
@@ -3319,7 +3335,6 @@ static void pci_unmap_srb_sense(struct AdapterCtlBlk *acb,
 	    srb->segment_x[DC395x_MAX_SG_LISTENTRY - 1].address;
 	srb->segment_x[0].length =
 	    srb->segment_x[DC395x_MAX_SG_LISTENTRY - 1].length;
-	srb->virt_addr = srb->virt_addr_req;
 }
 
 
@@ -3713,8 +3728,6 @@ static void request_sense(struct AdapterCtlBlk *acb, struct DeviceCtlBlk *dcb,
 	srb->xferred = srb->total_xfer_length;
 	/* srb->segment_x : a one entry of S/G list table */
 	srb->total_xfer_length = sizeof(cmd->sense_buffer);
-	srb->virt_addr_req = srb->virt_addr;
-	srb->virt_addr = cmd->sense_buffer;
 	srb->segment_x[0].length = sizeof(cmd->sense_buffer);
 	/* Map sense buffer */
 	srb->segment_x[0].address =

drivers/scsi/scsi_lib.c

@@ -2350,3 +2350,60 @@ scsi_target_unblock(struct device *dev)
 		device_for_each_child(dev, NULL, target_unblock);
 }
 EXPORT_SYMBOL_GPL(scsi_target_unblock);
+
+/**
+ * scsi_kmap_atomic_sg - find and atomically map an sg-elemnt
+ * @sg:		scatter-gather list
+ * @sg_count:	number of segments in sg
+ * @offset:	offset in bytes into sg, on return offset into the mapped area
+ * @len:	bytes to map, on return number of bytes mapped
+ *
+ * Returns virtual address of the start of the mapped page
+ */
+void *scsi_kmap_atomic_sg(struct scatterlist *sg, int sg_count,
+			  size_t *offset, size_t *len)
+{
+	int i;
+	size_t sg_len = 0, len_complete = 0;
+	struct page *page;
+
+	for (i = 0; i < sg_count; i++) {
+		len_complete = sg_len; /* Complete sg-entries */
+		sg_len += sg[i].length;
+		if (sg_len > *offset)
+			break;
+	}
+
+	if (unlikely(i == sg_count)) {
+		printk(KERN_ERR "%s: Bytes in sg: %u, requested offset %u, elements %d\n",
+		       __FUNCTION__, sg_len, *offset, sg_count);
+		WARN_ON(1);
+		return NULL;
+	}
+
+	/* Offset starting from the beginning of first page in this sg-entry */
+	*offset = *offset - len_complete + sg[i].offset;
+
+	/* Assumption: contiguous pages can be accessed as "page + i" */
+	page = nth_page(sg[i].page, (*offset >> PAGE_SHIFT));
+	*offset &= ~PAGE_MASK;
+
+	/* Bytes in this sg-entry from *offset to the end of the page */
+	sg_len = PAGE_SIZE - *offset;
+	if (*len > sg_len)
+		*len = sg_len;
+
+	return kmap_atomic(page, KM_BIO_SRC_IRQ);
+}
+EXPORT_SYMBOL(scsi_kmap_atomic_sg);
+
+/**
+ * scsi_kunmap_atomic_sg - atomically unmap a virtual address, previously
+ *			   mapped with scsi_kmap_atomic_sg
+ * @virt:	virtual address to be unmapped
+ */
+void scsi_kunmap_atomic_sg(void *virt)
+{
+	kunmap_atomic(virt, KM_BIO_SRC_IRQ);
+}
+EXPORT_SYMBOL(scsi_kunmap_atomic_sg);

include/scsi/scsi_cmnd.h

@@ -152,4 +152,8 @@ extern void scsi_put_command(struct scsi_cmnd *);
 extern void scsi_io_completion(struct scsi_cmnd *, unsigned int, unsigned int);
 extern void scsi_finish_command(struct scsi_cmnd *cmd);
 
+extern void *scsi_kmap_atomic_sg(struct scatterlist *sg, int sg_count,
+				 size_t *offset, size_t *len);
+extern void scsi_kunmap_atomic_sg(void *virt);
+
 #endif /* _SCSI_SCSI_CMND_H */