firewire: ohci: remove superfluous posted write flushes

The call to flush_writes() in context_stop() is superfluous because
another register read is done immediately afterwards.

The call to flush_writes() in ar_context_run() does not need to be done
individually for each AR context, so move it to ohci_enable().  This
also makes ohci_enable() clearer because it no longer depends on a side
effect of ar_context_run() to flush its own register writes.

Finally, the setting of a context's wake bit does not need to be flushed
because neither the driver logic nor the API require the CPU to wait for
this action.  This removes the last MMIO reads from the packet queueing
code paths.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/ohci.c

@@ -629,7 +629,6 @@ static void ar_context_link_page(struct ar_context *ctx, unsigned int index)
 	ctx->last_buffer_index = index;
 
 	reg_write(ctx->ohci, CONTROL_SET(ctx->regs), CONTEXT_WAKE);
-	flush_writes(ctx->ohci);
 }
 
 static void ar_context_release(struct ar_context *ctx)
@@ -1001,7 +1000,6 @@ static void ar_context_run(struct ar_context *ctx)
 
 	reg_write(ctx->ohci, COMMAND_PTR(ctx->regs), ctx->descriptors_bus | 1);
 	reg_write(ctx->ohci, CONTROL_SET(ctx->regs), CONTEXT_RUN);
-	flush_writes(ctx->ohci);
 }
 
 static struct descriptor *find_branch_descriptor(struct descriptor *d, int z)
@@ -1201,7 +1199,6 @@ static void context_stop(struct context *ctx)
 
 	reg_write(ctx->ohci, CONTROL_CLEAR(ctx->regs), CONTEXT_RUN);
 	ctx->running = false;
-	flush_writes(ctx->ohci);
 
 	for (i = 0; i < 10; i++) {
 		reg = reg_read(ctx->ohci, CONTROL_SET(ctx->regs));
@@ -1345,12 +1342,10 @@ static int at_context_queue_packet(struct context *ctx,
 
 	context_append(ctx, d, z, 4 - z);
 
-	if (ctx->running) {
+	if (ctx->running)
 		reg_write(ohci, CONTROL_SET(ctx->regs), CONTEXT_WAKE);
-		flush_writes(ohci);
-	} else {
+	else
 		context_run(ctx, 0);
-	}
 
 	return 0;
 }
@@ -2196,7 +2191,9 @@ static int ohci_enable(struct fw_card *card,
 		  OHCI1394_LinkControl_rcvPhyPkt);
 
 	ar_context_run(&ohci->ar_request_ctx);
-	ar_context_run(&ohci->ar_response_ctx); /* also flushes writes */
+	ar_context_run(&ohci->ar_response_ctx);
+
+	flush_writes(ohci);
 
 	/* We are ready to go, reset bus to finish initialization. */
 	fw_schedule_bus_reset(&ohci->card, false, true);
@@ -3128,7 +3125,6 @@ static void ohci_flush_queue_iso(struct fw_iso_context *base)
 			&container_of(base, struct iso_context, base)->context;
 
 	reg_write(ctx->ohci, CONTROL_SET(ctx->regs), CONTEXT_WAKE);
-	flush_writes(ctx->ohci);
 }
 
 static const struct fw_card_driver ohci_driver = {