Re: [PATCH v3 4/6] drm/tinydrm: add support for LEGO MINDSTORMS EV3 LCD

Noralf Trønnes
2017-08-05T19:55:02Z

Den 05.08.2017 20.19, skrev Noralf Trønnes:
>
> Den 04.08.2017 00.33, skrev David Lechner:
>> LEGO MINDSTORMS EV3 has an LCD with a ST7586 controller. This adds a new
>> module for the ST7586 controller with parameters for the LEGO MINDSTORMS
>> EV3 LCD display.
>>
>> Signed-off-by: David Lechner <david@lechnology.com>
>> ---

[...]

>> diff --git a/drivers/gpu/drm/tinydrm/st7586.c
>> b/drivers/gpu/drm/tinydrm/st7586.c

[...]

>> +static void st7586_xrgb8888_to_gray332(u8 *dst, void *vaddr,
>
> Could you put a comment somewhere explaining what grey332 means, that
> it's not
> a 332 pixel format that I first thought, but that you store 3x 2-bit
> pixles in one byte.
>
>> + struct drm_framebuffer *fb,
>> + struct drm_clip_rect *clip)
>> +{
>> + size_t len = (clip->x2 - clip->x1) * (clip->y2 - clip->y1);
>> + unsigned int x, y;
>> + u8 *src, *buf, val;
>> +
>> + /* 3 pixels per byte, so grow clip to nearest multiple of 3 */
>> + clip->x1 = clip->x1 / 3 * 3;
>
> Something wrong here: 3 * 3.
>
>> + clip->x2 = (clip->x2 + 2) / 3 * 3;
>
> You can use DIV_ROUND_UP().
>

Now I see what you're doing, can you use roundup() and rounddown()?

>> +
>> + buf = kmalloc(len, GFP_KERNEL);
>> + if (!buf)
>> + return;
>> +
>> + tinydrm_xrgb8888_to_gray8(buf, vaddr, fb, clip);
>> + src = buf;
>> +
>> + for (y = clip->y1; y < clip->y2; y++) {
>> + for (x = clip->x1; x < clip->x2; x += 3) {
>> + val = *src++ & 0xc0;
>> + if (val & 0xc0)
>> + val |= 0x20;
>> + val |= (*src++ & 0xc0) >> 3;
>> + if (val & 0x18)
>> + val |= 0x04;
>> + val |= *src++ >> 6;
>> + *dst++ = ~val;
>
> I don't understand how this pixel packing matches the one described in
> the datasheet. Why do you flip the bits at the end?
>
>> + }
>> + }
>> +
>> + /* now adjust the clip so it applies to dst */
>> + clip->x1 /= 3;
>> + clip->x2 /= 3;

I don't like this, you are changing the clip into a buffer length.
Better do the calculation before you call mipi_dbi_command_buf().

>> +
>> + kfree(buf);
>> +}
>> +
>> +static int st7586_buf_copy(void *dst, struct drm_framebuffer *fb,
>> + struct drm_clip_rect *clip)
>> +{
>> + struct drm_gem_cma_object *cma_obj = drm_fb_cma_get_gem_obj(fb, 0);
>> + struct dma_buf_attachment *import_attach =
>> cma_obj->base.import_attach;
>> + struct drm_format_name_buf format_name;
>> + void *src = cma_obj->vaddr;
>> + int ret = 0;
>> +
>> + if (import_attach) {
>> + ret = dma_buf_begin_cpu_access(import_attach->dmabuf,
>> + DMA_FROM_DEVICE);
>> + if (ret)
>> + return ret;
>> + }
>> +
>> + switch (fb->format->format) {
>> + case DRM_FORMAT_XRGB8888:
>> + st7586_xrgb8888_to_gray332(dst, src, fb, clip);
>> + break;

I assume you will be adding monochrome and greyscale formats here soon.
Maybe you should have a function st7586_grey8_pack() or something, and do:

switch (fb->format->format) {
case DRM_FORMAT_XRGB8888:
buf = kmalloc();
tinydrm_xrgb8888_to_gray8(buf, src, fb, clip);
st7586_grey8_to_packed8(dst, buf, clip);
kfree();
break;

And then later add:

case DRM_FORMAT_Y8:
st7586_grey8_to_packed8(dst, src,...);
break;
case DRM_FORMAT_Y1:
st7586_mono_to_packed8(dst, src,...);
break;

Just a suggestion, feel free to do what you want.

A patch adding greyscale came today:
https://lists.freedesktop.org/archives/dri-devel/2017-August/149445.html

>> + default:
>> + dev_err_once(fb->dev->dev, "Format is not supported: %s\n",
>> + drm_get_format_name(fb->format->format,
>> + &format_name));
>> + ret = -EINVAL;
>> + break;
>
> You don't need this default, because you can only get the ones in
> st7586_formats.
>
>> + }
>> +
>> + if (import_attach)
>> + dma_buf_end_cpu_access(import_attach->dmabuf, DMA_FROM_DEVICE);
>
> ret = dma_buf_end_cpu_access(...)
>
>> +
>> + return ret;
>> +}
>> +
>> +static int st7586_fb_dirty(struct drm_framebuffer *fb,
>> + struct drm_file *file_priv, unsigned int flags,
>> + unsigned int color, struct drm_clip_rect *clips,
>> + unsigned int num_clips)
>> +{
>> + struct tinydrm_device *tdev = fb->dev->dev_private;
>> + struct mipi_dbi *mipi = mipi_dbi_from_tinydrm(tdev);
>> + struct drm_clip_rect clip;
>> + int ret = 0;
>> +
>> + mutex_lock(&tdev->dirty_lock);
>> +
>> + if (!mipi->enabled)
>> + goto out_unlock;
>> +
>> + /* fbdev can flush even when we're not interested */
>> + if (tdev->pipe.plane.fb != fb)
>> + goto out_unlock;
>> +
>> + tinydrm_merge_clips(&clip, clips, num_clips, flags, fb->width,
>> + fb->height);
>> +

I suggest you adjust the clip here since it applies to all formats:

/* pixels are packed in threes */
clip->x1 = rounddown(clip->x1, 3);
clip->x2 = roundup(clip->x2, 3);

>> + DRM_DEBUG("Flushing [FB:%d] x1=%u, x2=%u, y1=%u, y2=%u\n",
>> fb->base.id,
>> + clip.x1, clip.x2, clip.y1, clip.y2);
>> +
>> + ret = st7586_buf_copy(mipi->tx_buf, fb, &clip);
>> + if (ret)
>> + goto out_unlock;
>> +
>> + /* NB: st7586_buf_copy() modifies clip */
>> +
>> + mipi_dbi_command(mipi, MIPI_DCS_SET_COLUMN_ADDRESS,
>> + (clip.x1 >> 8) & 0xFF, clip.x1 & 0xFF,
>> + (clip.x2 >> 8) & 0xFF, (clip.x2 - 1) & 0xFF);
>> + mipi_dbi_command(mipi, MIPI_DCS_SET_PAGE_ADDRESS,
>> + (clip.y1 >> 8) & 0xFF, clip.y1 & 0xFF,
>> + (clip.y2 >> 8) & 0xFF, (clip.y2 - 1) & 0xFF);
>> +
>> + ret = mipi_dbi_command_buf(mipi, MIPI_DCS_WRITE_MEMORY_START,
>> + (u8 *)mipi->tx_buf,
>> + (clip.x2 - clip.x1) * (clip.y2 - clip.y1));
>> +
>> +out_unlock:
>> + mutex_unlock(&tdev->dirty_lock);
>> +
>> + if (ret)
>> + dev_err_once(fb->dev->dev, "Failed to update display %d\n",
>> + ret);
>> +
>> + return ret;
>> +}
>> +