Re: [PATCH v3 2/7] drm/format-helper: Add drm_fb_{xrgb8888, gray8}_to_mono_reversed()

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi

Am 09.02.22 um 14:26 schrieb Javier Martinez Canillas:
Hello Thomas,

Thanks a lot for your feedback.

On 2/9/22 13:51, Thomas Zimmermann wrote:
Hi


[snip]

+
+		if (xb == pixels - 1 && end_offset)
+			end = end_offset;

end_offset should be called end_len, because it is the number of bits in
the final byte; but not the offset of the final bit.


Indeed.

[snip]

+void drm_fb_gray8_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *vaddr,
+				   const struct drm_framebuffer *fb,
+				   const struct drm_rect *clip)

[snip]


Do you really need that function. It's not exported and if it's not
otherwise used, I'd just remove it.  We don't keep unused interfaces around.


At the end after your suggestion of doing line-per-line conversions it is not
needed, but since I already typed it and we were talking about adding other
formats besides the fake XRGB8888 as an optimization (R8 for grayscale and
Dx or something like that for reversed mono), I thought that would be useful
to have it as a helper.

Also other drivers that want to advertise a R8 format could just use it and
not having to add their own helper. But I'm happy to drop it in v4 if you
think that's better to not have unused helpers.

It could be taken from this patch-set anyways if someone wants to wire the
needed support for R8.

I think, policy is to not keep unused code around.


[snip]

+
+	/*
+	 * The reversed mono destination buffer contains 1 bit per pixel
+	 * and destination scanlines have to be in multiple of 8 pixels.
+	 */
+	if (!dst_pitch)
+		dst_pitch = DIV_ROUND_UP(linepixels, 8);

I'd do a warn_once if (dst_pitch % 8 != 0).


Agreed. I'll add a warning an mention that will be rounded up.


+
+	/*
+	 * The cma memory is write-combined so reads are uncached.
+	 * Speed up by fetching one line at a time.

I once had a patchset that adds caching information to struct
dma_buf_map (soon to be named struct iosys_map).  Blitting helpers would
be able to enable/disable this optimization as needed.

However, your driver doesn't use CMA. It's backed by SHMEM. Do you
really want to keep that code in?


It doesn't but the repaper does. And since the plan was to make that driver
to use the helper instead of having their own, I wanted to also make sure
that would work well with CMA.

That makes sense then.



+	 */
+	src32 = kmalloc(len_src32, GFP_KERNEL);
+	if (!src32)
+		return;
+
+	/*
+	 * Copies are done line-by-line, allocate an intermediate
+	 * buffer to copy the gray8 lines and then convert to mono.
+	 */
+	gray8 = kmalloc(linepixels, GFP_KERNEL);
+	if (!gray8)
+		goto free_src32;

If might be faster to allocate both buffers in one step and set the
pointers into the allocated buffer.


Not sure I got this. Do you mean to have a single buffer with length
linepixels + len_src32 and point src32 and gray8 to the same buffer ?

That's the idea. I don't know the exact overhead for kalloc(), but at least the in userspace, malloc() in hot code paths is not a good idea. There's usually some searching for free space involved.

In the long term, we could add a field in struct drm_framebuffer to keep such buffers around for reuse.


+
+	/*
+	 * For damage handling, it is possible that only parts of the source
+	 * buffer is copied and this could lead to start and end pixels that
+	 * are not aligned to multiple of 8.
+	 *
+	 * Calculate if the start and end pixels are not aligned and set the
+	 * offsets for the reversed mono line conversion function to adjust.
+	 */
+	start_offset = clip->x1 % 8;
+	end_offset = clip->x2 % 8;

end_len, again. If you have 1 single bit set in the final byte, the
offset is 0, but the length is 1.


Agreed, will change it too.

Feel free to add my

Reviewed-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

to the next version.

Best regards
Thomas


Best regards,

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

Attachment: OpenPGP_signature
Description: OpenPGP digital signature


[Index of Archives]     [Linux DRI Users]     [Linux Intel Graphics]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [XFree86]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux