Re: [RFC PATCH v2 1/3] drm/fourcc: Add 'bpp' field for formats with non-integer bytes-per-pixel

Brian Starkey <brian.starkey@xxxxxxx> · Fri, 7 Sep 2018 13:45:36 +0100

Hi Daniel,

On Fri, Aug 31, 2018 at 10:17:30AM +0200, Daniel Vetter wrote:
On Thu, Aug 23, 2018 at 04:23:41PM +0100, Brian Starkey wrote:
Some formats have a non-integer number of bytes per pixel, which can't
be handled with the existing 'cpp' field in drm_format_info. To handle
these formats, add a 'bpp' field, which is only used if cpp[0] == 0.

This updates all the users of format->cpp in the core DRM code,
converting them to use a new function to get the bits-per-pixel for any
format.

It's assumed that drivers will use the 'bpp' field when they add support
for pixel formats with non-integer bytes-per-pixel.

Signed-off-by: Brian Starkey <brian.starkey@xxxxxxx>

I assume you still require that stuff is eventually aligned to bytes? In
that case, can we subsume this into the tile work Alex is doing? It's
essentially just another special case of having storage-size units
measured in bytes which span more than 1x1 pixel. And I kinda don't want a
metric pile of special cases here in the format code, because that just
means every driver handles a different subset, with different bugs.
-Daniel

Sorry for the delay, been struggling to free some cycles to think
about this.

I'm not sure how to pull this in with the tiling stuff. In the AFBC
case then our AFBC superblocks are always nice round numbers (256
pixels), and so it does end up being a multiple of bytes.

However, AFBC supports different superblock sizes, so picking just one
doesn't really work out, and putting AFBC in the core format table
which reflects AFBC doesn't seem good.

We could make something up (e.g. call these formats "tiled" with 2x4
tiles, which guarantees a multiple of 8), but it would be an
arbitrarily-selected lie, which often seems to spell trouble. If we
did do that, would you re-define cpp as "bytes-per-tile"? Otherwise
we still need to add a new field anyway.

What's the pile of special cases you're worried about? The helper I've
added here means that drivers which need to care can use one API and
not implement their own bugs.

Cheers,
-Brian


---
 drivers/gpu/drm/drm_fb_cma_helper.c          |  6 +++-
 drivers/gpu/drm/drm_fb_helper.c              |  8 +++--
 drivers/gpu/drm/drm_fourcc.c                 | 50 ++++++++++++++++++++++++++++
 drivers/gpu/drm/drm_framebuffer.c            |  8 ++---
 drivers/gpu/drm/drm_gem_framebuffer_helper.c |  3 +-
 include/drm/drm_fourcc.h                     |  4 +++
 6 files changed, 70 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
index 186d00adfb5f..e279d70d3e60 100644
--- a/drivers/gpu/drm/drm_fb_cma_helper.c
+++ b/drivers/gpu/drm/drm_fb_cma_helper.c
@@ -118,13 +118,17 @@ dma_addr_t drm_fb_cma_get_gem_addr(struct drm_framebuffer *fb,
 {
 	struct drm_gem_cma_object *obj;
 	dma_addr_t paddr;
+	u8 bpp = drm_format_info_plane_bpp(fb->format, plane);
+
+	/* This can't work for non-integer bytes-per-pixel */
+	WARN_ON(bpp % 8);

 	obj = drm_fb_cma_get_gem_obj(fb, plane);
 	if (!obj)
 		return 0;

 	paddr = obj->paddr + fb->offsets[plane];
-	paddr += fb->format->cpp[plane] * (state->src_x >> 16);
+	paddr += (bpp / 8) * (state->src_x >> 16);
 	paddr += fb->pitches[plane] * (state->src_y >> 16);

 	return paddr;
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 0646b108030b..ab369f250af4 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1572,6 +1572,7 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 	struct drm_fb_helper *fb_helper = info->par;
 	struct drm_framebuffer *fb = fb_helper->fb;
 	int depth;
+	u8 bpp = drm_format_info_plane_bpp(fb->format, 0);

 	if (var->pixclock != 0 || in_dbg_master())
 		return -EINVAL;
@@ -1580,14 +1581,14 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 	 * Changes struct fb_var_screeninfo are currently not pushed back
 	 * to KMS, hence fail if different settings are requested.
 	 */
-	if (var->bits_per_pixel != fb->format->cpp[0] * 8 ||
+	if (var->bits_per_pixel != bpp ||
 	    var->xres > fb->width || var->yres > fb->height ||
 	    var->xres_virtual > fb->width || var->yres_virtual > fb->height) {
 		DRM_DEBUG("fb requested width/height/bpp can't fit in current fb "
 			  "request %dx%d-%d (virtual %dx%d) > %dx%d-%d\n",
 			  var->xres, var->yres, var->bits_per_pixel,
 			  var->xres_virtual, var->yres_virtual,
-			  fb->width, fb->height, fb->format->cpp[0] * 8);
+			  fb->width, fb->height, bpp);
 		return -EINVAL;
 	}

@@ -1949,11 +1950,12 @@ void drm_fb_helper_fill_var(struct fb_info *info, struct drm_fb_helper *fb_helpe
 			    uint32_t fb_width, uint32_t fb_height)
 {
 	struct drm_framebuffer *fb = fb_helper->fb;
+	u8 bpp = drm_format_info_plane_bpp(fb->format, 0);

 	info->pseudo_palette = fb_helper->pseudo_palette;
 	info->var.xres_virtual = fb->width;
 	info->var.yres_virtual = fb->height;
-	info->var.bits_per_pixel = fb->format->cpp[0] * 8;
+	info->var.bits_per_pixel = bpp;
 	info->var.accel_flags = FB_ACCELF_TEXT;
 	info->var.xoffset = 0;
 	info->var.yoffset = 0;
diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
index 3b42c25bd58d..bb28919c32f3 100644
--- a/drivers/gpu/drm/drm_fourcc.c
+++ b/drivers/gpu/drm/drm_fourcc.c
@@ -272,10 +272,60 @@ int drm_format_plane_cpp(uint32_t format, int plane)
 	if (!info || plane >= info->num_planes)
 		return 0;

+	/*
+	 * Not valid for formats with non-integer cpp,
+	 * use drm_format{_info}_plane_bpp instead
+	 */
+	WARN_ON(!info->cpp[0]);
+
 	return info->cpp[plane];
 }
 EXPORT_SYMBOL(drm_format_plane_cpp);

+/**
+ * drm_format_plane_bpp - determine the bits per pixel value
+ * @format: pixel format (DRM_FORMAT_*)
+ * @plane: plane index
+ *
+ * Returns:
+ * The bits per pixel value for the specified plane.
+ */
+int drm_format_plane_bpp(uint32_t format, int plane)
+{
+	const struct drm_format_info *info;
+
+	info = drm_format_info(format);
+	if (!info)
+		return 0;
+
+	return drm_format_info_plane_bpp(info, plane);
+}
+EXPORT_SYMBOL(drm_format_plane_bpp);
+
+/**
+ * drm_format_info_plane_bpp - determine the bits per pixel value
+ *
+ * Convenience function which handles formats with both integer
+ * and non-integer bytes-per-pixel.
+ *
+ * @format: pixel format info structure
+ * @plane: plane index
+ *
+ * Returns:
+ * The bits per pixel value for the specified plane.
+ */
+int drm_format_info_plane_bpp(const struct drm_format_info *info, int plane)
+{
+	if (plane >= info->num_planes)
+		return 0;
+
+	if (info->cpp[0])
+		return info->cpp[plane] * 8;
+
+	return info->bpp[plane];
+}
+EXPORT_SYMBOL(drm_format_info_plane_bpp);
+
 /**
  * drm_format_horz_chroma_subsampling - get the horizontal chroma subsampling factor
  * @format: pixel format (DRM_FORMAT_*)
diff --git a/drivers/gpu/drm/drm_framebuffer.c b/drivers/gpu/drm/drm_framebuffer.c
index 8c4d32adcc17..7e00360ff70d 100644
--- a/drivers/gpu/drm/drm_framebuffer.c
+++ b/drivers/gpu/drm/drm_framebuffer.c
@@ -185,20 +185,20 @@ static int framebuffer_check(struct drm_device *dev,
 	for (i = 0; i < info->num_planes; i++) {
 		unsigned int width = fb_plane_width(r->width, info, i);
 		unsigned int height = fb_plane_height(r->height, info, i);
-		unsigned int cpp = info->cpp[i];
+		unsigned int bpp = drm_format_info_plane_bpp(info, i);

 		if (!r->handles[i]) {
 			DRM_DEBUG_KMS("no buffer object handle for plane %d\n", i);
 			return -EINVAL;
 		}

-		if ((uint64_t) width * cpp > UINT_MAX)
+		if ((uint64_t) DIV_ROUND_UP(width * bpp, 8) > UINT_MAX)
 			return -ERANGE;

 		if ((uint64_t) height * r->pitches[i] + r->offsets[i] > UINT_MAX)
 			return -ERANGE;

-		if (r->pitches[i] < width * cpp) {
+		if ((uint64_t) r->pitches[i] * 8 < (uint64_t) width * bpp) {
 			DRM_DEBUG_KMS("bad pitch %u for plane %d\n", r->pitches[i], i);
 			return -EINVAL;
 		}
@@ -476,7 +476,7 @@ int drm_mode_getfb(struct drm_device *dev,
 	r->height = fb->height;
 	r->width = fb->width;
 	r->depth = fb->format->depth;
-	r->bpp = fb->format->cpp[0] * 8;
+	r->bpp = drm_format_info_plane_bpp(fb->format, 0);
 	r->pitch = fb->pitches[0];

 	/* GET_FB() is an unprivileged ioctl so we must not return a
diff --git a/drivers/gpu/drm/drm_gem_framebuffer_helper.c b/drivers/gpu/drm/drm_gem_framebuffer_helper.c
index acfbc0641a06..dfe224ccaeba 100644
--- a/drivers/gpu/drm/drm_gem_framebuffer_helper.c
+++ b/drivers/gpu/drm/drm_gem_framebuffer_helper.c
@@ -161,6 +161,7 @@ drm_gem_fb_create_with_funcs(struct drm_device *dev, struct drm_file *file,
 		unsigned int width = mode_cmd->width / (i ? info->hsub : 1);
 		unsigned int height = mode_cmd->height / (i ? info->vsub : 1);
 		unsigned int min_size;
+		u8 bpp = drm_format_info_plane_bpp(fb->format, i);

 		objs[i] = drm_gem_object_lookup(file, mode_cmd->handles[i]);
 		if (!objs[i]) {
@@ -170,7 +171,7 @@ drm_gem_fb_create_with_funcs(struct drm_device *dev, struct drm_file *file,
 		}

 		min_size = (height - 1) * mode_cmd->pitches[i]
-			 + width * info->cpp[i]
+			 + DIV_ROUND_UP(width * bpp, 8)
 			 + mode_cmd->offsets[i];

 		if (objs[i]->size < min_size) {
diff --git a/include/drm/drm_fourcc.h b/include/drm/drm_fourcc.h
index 3e86408dac9f..d4af4dab1623 100644
--- a/include/drm/drm_fourcc.h
+++ b/include/drm/drm_fourcc.h
@@ -36,6 +36,7 @@ struct drm_mode_fb_cmd2;
  *	use in new code and set to 0 for new formats.
  * @num_planes: Number of color planes (1 to 3)
  * @cpp: Number of bytes per pixel (per plane)
+ * @bpp: Number of bits per pixel (per plane), only valid if cpp[0] == 0.
  * @hsub: Horizontal chroma subsampling factor
  * @vsub: Vertical chroma subsampling factor
  * @has_alpha: Does the format embeds an alpha component?
@@ -45,6 +46,7 @@ struct drm_format_info {
 	u8 depth;
 	u8 num_planes;
 	u8 cpp[3];
+	u8 bpp[3];
 	u8 hsub;
 	u8 vsub;
 	bool has_alpha;
@@ -66,6 +68,8 @@ drm_get_format_info(struct drm_device *dev,
 uint32_t drm_mode_legacy_fb_format(uint32_t bpp, uint32_t depth);
 int drm_format_num_planes(uint32_t format);
 int drm_format_plane_cpp(uint32_t format, int plane);
+int drm_format_plane_bpp(uint32_t format, int plane);
+int drm_format_info_plane_bpp(const struct drm_format_info *format, int plane);
 int drm_format_horz_chroma_subsampling(uint32_t format);
 int drm_format_vert_chroma_subsampling(uint32_t format);
 int drm_format_plane_width(int width, uint32_t format, int plane);
--
2.16.1


--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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