drm: mxsfb: Implement LCDIF scanout CRC32 support

The LCDIF controller as present in i.MX28/i.MX6SX/i.MX8M Mini/Nano has
CRC_STAT register, which contains CRC32 of the frame as it was clocked
out of the DPI interface of the LCDIF. This is most likely meant as a
functional safety feature.

Unfortunately, there is zero documentation on how the CRC32 is calculated,
there is no documentation of the polynomial, the init value, nor on which
data is the checksum applied.

By applying brute-force on 8 pixel / 2 line frame, which is the minimum
size LCDIF would work with, it turns out the polynomial is CRC32_POLY_LE
0xedb88320 , init value is 0xffffffff , the input data are bitrev32()
of the entire frame and the resulting CRC has to be also bitrev32()ed.

Doing this calculation in kernel for each frame is unrealistic due to the
CPU demand, so attach the CRC collected from hardware to a frame instead.
The DRM subsystem already has an interface for this purpose and the CRC
can be accessed e.g. via debugfs:
"
$ echo auto > /sys/kernel/debug/dri/1/crtc-0/crc/control
$ cat /sys/kernel/debug/dri/1/crtc-0/crc/data
0x0000408c 0xa4e5cdd8
0x0000408d 0x72f537b4
"
The per-frame CRC can be used by userspace e.g. during automated testing,
to verify that whatever buffer was sent to be scanned out was actually
scanned out of the LCDIF correctly.
Acked-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexander Stein <alexander.stein@ew.tq-group.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Robby Cai <robby.cai@nxp.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Stefan Agner <stefan@agner.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220429212313.305556-1-marex@denx.de

drivers/gpu/drm/mxsfb/mxsfb_drv.c

@@ -52,6 +52,7 @@ static const struct mxsfb_devdata mxsfb_devdata[] = {
 		.hs_wdth_shift	= 24,
 		.has_overlay	= false,
 		.has_ctrl2	= false,
+		.has_crc32	= false,
 	},
 	[MXSFB_V4] = {
 		.transfer_count	= LCDC_V4_TRANSFER_COUNT,
@@ -61,6 +62,7 @@ static const struct mxsfb_devdata mxsfb_devdata[] = {
 		.hs_wdth_shift	= 18,
 		.has_overlay	= false,
 		.has_ctrl2	= true,
+		.has_crc32	= true,
 	},
 	[MXSFB_V6] = {
 		.transfer_count	= LCDC_V4_TRANSFER_COUNT,
@@ -70,6 +72,7 @@ static const struct mxsfb_devdata mxsfb_devdata[] = {
 		.hs_wdth_shift	= 18,
 		.has_overlay	= true,
 		.has_ctrl2	= true,
+		.has_crc32	= true,
 	},
 };
 
@@ -157,12 +160,19 @@ static irqreturn_t mxsfb_irq_handler(int irq, void *data)
 {
 	struct drm_device *drm = data;
 	struct mxsfb_drm_private *mxsfb = drm->dev_private;
-	u32 reg;
+	u32 reg, crc;
+	u64 vbc;
 
 	reg = readl(mxsfb->base + LCDC_CTRL1);
 
-	if (reg & CTRL1_CUR_FRAME_DONE_IRQ)
+	if (reg & CTRL1_CUR_FRAME_DONE_IRQ) {
 		drm_crtc_handle_vblank(&mxsfb->crtc);
+		if (mxsfb->crc_active) {
+			crc = readl(mxsfb->base + LCDC_V4_CRC_STAT);
+			vbc = drm_crtc_accurate_vblank_count(&mxsfb->crtc);
+			drm_crtc_add_crc_entry(&mxsfb->crtc, true, vbc, &crc);
+		}
+	}
 
 	writel(CTRL1_CUR_FRAME_DONE_IRQ, mxsfb->base + LCDC_CTRL1 + REG_CLR);
 

drivers/gpu/drm/mxsfb/mxsfb_drv.h

@@ -23,6 +23,7 @@ struct mxsfb_devdata {
 	unsigned int	hs_wdth_shift;
 	bool		has_overlay;
 	bool		has_ctrl2;
+	bool		has_crc32;
 };
 
 struct mxsfb_drm_private {
@@ -44,6 +45,8 @@ struct mxsfb_drm_private {
 	struct drm_encoder		encoder;
 	struct drm_connector		*connector;
 	struct drm_bridge		*bridge;
+
+	bool				crc_active;
 };
 
 static inline struct mxsfb_drm_private *

drivers/gpu/drm/mxsfb/mxsfb_kms.c

@@ -439,6 +439,41 @@ static void mxsfb_crtc_disable_vblank(struct drm_crtc *crtc)
 	writel(CTRL1_CUR_FRAME_DONE_IRQ, mxsfb->base + LCDC_CTRL1 + REG_CLR);
 }
 
+static int mxsfb_crtc_set_crc_source(struct drm_crtc *crtc, const char *source)
+{
+	struct mxsfb_drm_private *mxsfb;
+
+	if (!crtc)
+		return -ENODEV;
+
+	mxsfb = to_mxsfb_drm_private(crtc->dev);
+
+	if (source && strcmp(source, "auto") == 0)
+		mxsfb->crc_active = true;
+	else if (!source)
+		mxsfb->crc_active = false;
+	else
+		return -EINVAL;
+
+	return 0;
+}
+
+static int mxsfb_crtc_verify_crc_source(struct drm_crtc *crtc,
+					const char *source, size_t *values_cnt)
+{
+	if (!crtc)
+		return -ENODEV;
+
+	if (source && strcmp(source, "auto") != 0) {
+		DRM_DEBUG_DRIVER("Unknown CRC source %s for %s\n",
+				 source, crtc->name);
+		return -EINVAL;
+	}
+
+	*values_cnt = 1;
+	return 0;
+}
+
 static const struct drm_crtc_helper_funcs mxsfb_crtc_helper_funcs = {
 	.atomic_check = mxsfb_crtc_atomic_check,
 	.atomic_flush = mxsfb_crtc_atomic_flush,
@@ -457,6 +492,19 @@ static const struct drm_crtc_funcs mxsfb_crtc_funcs = {
 	.disable_vblank = mxsfb_crtc_disable_vblank,
 };
 
+static const struct drm_crtc_funcs mxsfb_crtc_with_crc_funcs = {
+	.reset = drm_atomic_helper_crtc_reset,
+	.destroy = drm_crtc_cleanup,
+	.set_config = drm_atomic_helper_set_config,
+	.page_flip = drm_atomic_helper_page_flip,
+	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
+	.enable_vblank = mxsfb_crtc_enable_vblank,
+	.disable_vblank = mxsfb_crtc_disable_vblank,
+	.set_crc_source = mxsfb_crtc_set_crc_source,
+	.verify_crc_source = mxsfb_crtc_verify_crc_source,
+};
+
 /* -----------------------------------------------------------------------------
  * Encoder
  */
@@ -645,9 +693,16 @@ int mxsfb_kms_init(struct mxsfb_drm_private *mxsfb)
 	}
 
 	drm_crtc_helper_add(crtc, &mxsfb_crtc_helper_funcs);
-	ret = drm_crtc_init_with_planes(mxsfb->drm, crtc,
-					&mxsfb->planes.primary, NULL,
-					&mxsfb_crtc_funcs, NULL);
+	if (mxsfb->devdata->has_crc32) {
+		ret = drm_crtc_init_with_planes(mxsfb->drm, crtc,
+						&mxsfb->planes.primary, NULL,
+						&mxsfb_crtc_with_crc_funcs,
+						NULL);
+	} else {
+		ret = drm_crtc_init_with_planes(mxsfb->drm, crtc,
+						&mxsfb->planes.primary, NULL,
+						&mxsfb_crtc_funcs, NULL);
+	}
 	if (ret)
 		return ret;
 

drivers/gpu/drm/mxsfb/mxsfb_regs.h

@@ -26,6 +26,7 @@
 #define LCDC_VDCTRL2			0x90
 #define LCDC_VDCTRL3			0xa0
 #define LCDC_VDCTRL4			0xb0
+#define LCDC_V4_CRC_STAT		0x1a0
 #define LCDC_V4_DEBUG0			0x1d0
 #define LCDC_V3_DEBUG0			0x1f0
 #define LCDC_AS_CTRL			0x210