Re: [PATCH v2 4/8] drm/ssd130x: Add support for DRM_FORMAT_R1

[Geert Uytterhoeven]

Hi Thomas,

On Thu, Aug 31, 2023 at 10:01 AM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> Am 24.08.23 um 17:08 schrieb Geert Uytterhoeven:
> > The native display format is monochrome light-on-dark (R1).
> > Hence add support for R1, so monochrome applications not only look
> > better, but also avoid the overhead of back-and-forth conversions
> > between R1 and XR24.
> >
> > Do not allocate the intermediate conversion buffer when it is not
> > needed, and reorder the two buffer allocations to streamline operation.
> >
> > Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > ---
> > v2:
> >    - Rework on top op commit 8c3926367ac9df6c ("drm/ssd130x: Use
> >      shadow-buffer helpers when managing plane's state") in drm/drm-next.
> >      Hence I did not add Javier's tags given on v1.
> >    - Do not allocate intermediate buffer when not needed.
> > ---
> >   drivers/gpu/drm/solomon/ssd130x.c | 76 +++++++++++++++++++++----------
> >   1 file changed, 51 insertions(+), 25 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/solomon/ssd130x.c b/drivers/gpu/drm/solomon/ssd130x.c
> > index 78272b1f9d5b167f..18007cb4f3de5aa1 100644
> > --- a/drivers/gpu/drm/solomon/ssd130x.c
> > +++ b/drivers/gpu/drm/solomon/ssd130x.c
> > @@ -449,15 +449,14 @@ static int ssd130x_init(struct ssd130x_device *ssd130x)
> >
> >   static int ssd130x_update_rect(struct ssd130x_device *ssd130x,
> >                              struct ssd130x_plane_state *ssd130x_state,
> > +                            u8 *buf, unsigned int pitch,
> >                              struct drm_rect *rect)
> >   {
> >       unsigned int x = rect->x1;
> >       unsigned int y = rect->y1;
> > -     u8 *buf = ssd130x_state->buffer;
> >       u8 *data_array = ssd130x_state->data_array;
> >       unsigned int width = drm_rect_width(rect);
> >       unsigned int height = drm_rect_height(rect);
> > -     unsigned int line_length = DIV_ROUND_UP(width, 8);
> >       unsigned int page_height = ssd130x->device_info->page_height;
> >       unsigned int pages = DIV_ROUND_UP(height, page_height);
> >       struct drm_device *drm = &ssd130x->drm;
> > @@ -516,7 +515,7 @@ static int ssd130x_update_rect(struct ssd130x_device *ssd130x,
> >                       u8 data = 0;
> >
> >                       for (k = 0; k < m; k++) {
> > -                             u8 byte = buf[(8 * i + k) * line_length + j / 8];
> > +                             u8 byte = buf[(8 * i + k) * pitch + j / 8];
> >                               u8 bit = (byte >> (j % 8)) & 1;
> >
> >                               data |= bit << k;
> > @@ -602,27 +601,51 @@ static int ssd130x_fb_blit_rect(struct drm_plane_state *state,
>
> The handing of different formats in this function is confusing. I'd
> rather implement ssd130x_fb_blit_rect_r1 and
> ssd130x_fb_blit_rect_xrgb8888 which then handle a single format.

OK, will split.

> >       struct ssd130x_device *ssd130x = drm_to_ssd130x(fb->dev);
> >       unsigned int page_height = ssd130x->device_info->page_height;
> >       struct ssd130x_plane_state *ssd130x_state = to_ssd130x_plane_state(state);
> > -     u8 *buf = ssd130x_state->buffer;
> >       struct iosys_map dst;
> >       unsigned int dst_pitch;
> >       int ret = 0;
> > +     u8 *buf;
> >
> >       /* Align y to display page boundaries */
> >       rect->y1 = round_down(rect->y1, page_height);
> >       rect->y2 = min_t(unsigned int, round_up(rect->y2, page_height), ssd130x->height);
> >
> > -     dst_pitch = DIV_ROUND_UP(drm_rect_width(rect), 8);
> > +     switch (fb->format->format) {
> > +     case DRM_FORMAT_R1:
> > +             /* Align x to byte boundaries */
> > +             rect->x1 = round_down(rect->x1, 8);
> > +             rect->x2 = round_up(rect->x2, 8);
>
> Is rounding to multiples of 8 guaranteed to work? I know it did on
> VGA-compatible HW, because VGA enforces it. But is that generally the case?

That depends: some hardware requires e.g. 32-bit writes.
But this driver is for a display with a serial (i2c/spi) interface,
so everything should be fine ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds