Re: [PATCH 07/10] drm/format-helper: Add drm_fb_swab()

Noralf Trønnes
2020-05-03T13:38:49Z

Den 03.05.2020 12.29, skrev Sam Ravnborg:
> Hi Noralf
>
> On Wed, Apr 29, 2020 at 02:48:27PM +0200, Noralf Trønnes wrote:
>> This replaces drm_fb_swab16() with drm_fb_swab() supporting 16 and 32-bit.
>> Also make pixel line caching optional.
>>
>> Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
> A couple of nits, with these considered:
> Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
>
>> ---
>> drivers/gpu/drm/drm_format_helper.c | 61 +++++++++++++++++++----------
>> drivers/gpu/drm/drm_mipi_dbi.c | 2 +-
>> include/drm/drm_format_helper.h | 4 +-
>> 3 files changed, 44 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
>> index 0897cb9aeaff..5c147c49668c 100644
>> --- a/drivers/gpu/drm/drm_format_helper.c
>> +++ b/drivers/gpu/drm/drm_format_helper.c
>> @@ -79,39 +79,60 @@ void drm_fb_memcpy_dstclip(void __iomem *dst, void *vaddr,
>> EXPORT_SYMBOL(drm_fb_memcpy_dstclip);
>>
>> /**
>> - * drm_fb_swab16 - Swap bytes into clip buffer
>> - * @dst: RGB565 destination buffer
>> - * @vaddr: RGB565 source buffer
>> + * drm_fb_swab - Swap bytes into clip buffer
>> + * @dst: Destination buffer
>> + * @src: Source buffer
>> * @fb: DRM framebuffer
>> * @clip: Clip rectangle area to copy
>> + * @cached: Source buffer is mapped cached (eg. not write-combined)
>> + *
>> + * If @cached is false a temporary buffer is used to cache one pixel line at a
>> + * time to speed up slow uncached reads.
>> + *
>> + * This function does not apply clipping on dst, i.e. the destination
>> + * is a small buffer containing the clip rect only.
>> */
>> -void drm_fb_swab16(u16 *dst, void *vaddr, struct drm_framebuffer *fb,
>> - struct drm_rect *clip)
>> +void drm_fb_swab(void *dst, void *src, struct drm_framebuffer *fb,
>> + struct drm_rect *clip, bool cached)
>> {
>> - size_t len = (clip->x2 - clip->x1) * sizeof(u16);
>> + u8 cpp = fb->format->cpp[0];
> Use of format->cpp is deprecated, should be char_per_block according to
> the comment in drm_fourcc.h

I ducked this because if I had to do it properly I would have to look at
block width/height as well and yes ensure that num_planes is 1. That
would leave me with writing a helper function for something I don't
really understand :-)

static inline bool
drm_format_info_is_WHAT_TO_CALL_THIS(const struct drm_format_info *info)
{
return info->num_planes == 1 &&
drm_format_info_block_width(info, 0) == 1 &&
drm_format_info_block_height(info, 0) == 1;
}

Or I could ofc just spell out the full assert inside this function:

info->num_planes == 1 &&
drm_format_info_block_width(info, 0) == 1 &&
drm_format_info_block_height(info, 0) == 1 &&
info->char_per_block[0] == 2 &&
info->char_per_block[0] == 4

That way I don't have to know what I'm actually checking.
I'm using drm_fb_swab() for RGB formats, but it can be used for any
format that meets the above criteria.

And maybe I should check .hsub and .vsub as well, I don't know.

cpp was such a nice simple concept :-) So I'll keep it unless someone
knowledgeable shines some light on this.

>
>> + size_t len = drm_rect_width(clip) * cpp;
>> + u16 *src16, *dst16 = dst;
>> + u32 *src32, *dst32 = dst;
>> unsigned int x, y;
>> - u16 *src, *buf;
>> + void *buf = NULL;
>>
>> - /*
>> - * The cma memory is write-combined so reads are uncached.
>> - * Speed up by fetching one line at a time.
>> - */
>> - buf = kmalloc(len, GFP_KERNEL);
>> - if (!buf)
>> + if (WARN_ON_ONCE(cpp == 1))
>> return;
> Or cpp != 2 && cpp != 4?

Indeed, I agree.

Noralf.

>>
>> + if (!cached)
>> + buf = kmalloc(len, GFP_KERNEL);
>> +
>> + src += clip_offset(clip, fb->pitches[0], cpp);
> Good that drm_rect_width() and clip_offset() are used,
> replacing open-coded variants.
>
>> +
>> for (y = clip->y1; y < clip->y2; y++) {
>> - src = vaddr + (y * fb->pitches[0]);
>> - src += clip->x1;
>> - memcpy(buf, src, len);
>> - src = buf;
>> - for (x = clip->x1; x < clip->x2; x++)
>> - *dst++ = swab16(*src++);
>> + if (buf) {
>> + memcpy(buf, src, len);
>> + src16 = buf;
>> + src32 = buf;
>> + } else {
>> + src16 = src;
>> + src32 = src;
>> + }
>> +
>> + for (x = clip->x1; x < clip->x2; x++) {
>> + if (cpp == 4)
>> + *dst32++ = swab32(*src32++);
>> + else
>> + *dst16++ = swab16(*src16++);
>> + }
>> +
>> + src += fb->pitches[0];
>> }
>>
>> kfree(buf);
>> }
>> -EXPORT_SYMBOL(drm_fb_swab16);
>> +EXPORT_SYMBOL(drm_fb_swab);
>>
>> static void drm_fb_xrgb8888_to_rgb565_line(u16 *dbuf, u32 *sbuf,
>> unsigned int pixels,
>> diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
>> index 16bff1be4b8a..bfefbcb69287 100644
>> --- a/drivers/gpu/drm/drm_mipi_dbi.c
>> +++ b/drivers/gpu/drm/drm_mipi_dbi.c
>> @@ -217,7 +217,7 @@ int mipi_dbi_buf_copy(void *dst, struct drm_framebuffer *fb,
>> switch (fb->format->format) {
>> case DRM_FORMAT_RGB565:
>> if (swap)
>> - drm_fb_swab16(dst, src, fb, clip);
>> + drm_fb_swab(dst, src, fb, clip, !import_attach);
>> else
>> drm_fb_memcpy(dst, src, fb, clip);
>> break;
>> diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
>> index ac220aa1a245..5f9e37032468 100644
>> --- a/include/drm/drm_format_helper.h
>> +++ b/include/drm/drm_format_helper.h
>> @@ -14,8 +14,8 @@ void drm_fb_memcpy(void *dst, void *vaddr, struct drm_framebuffer *fb,
>> void drm_fb_memcpy_dstclip(void __iomem *dst, void *vaddr,
>> struct drm_framebuffer *fb,
>> struct drm_rect *clip);
>> -void drm_fb_swab16(u16 *dst, void *vaddr, struct drm_framebuffer *fb,
>> - struct drm_rect *clip);
>> +void drm_fb_swab(void *dst, void *src, struct drm_framebuffer *fb,
>> + struct drm_rect *clip, bool cached);
>> void drm_fb_xrgb8888_to_rgb565(void *dst, void *vaddr,
>> struct drm_framebuffer *fb,
>> struct drm_rect *clip, bool swab);
>> --
>> 2.23.0
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel