[PATCH v5 9/9] drm/mediatek: dsi: Use mipi_dsi_pixel_format_to_bpp() helper function

[AngeloGioacchino Del Regno]

Instead of open coding, use the mipi_dsi_pixel_format_to_bpp() helper
function from drm_mipi_dsi.h in mtk_dsi_poweron() and for validation
in mtk_dsi_bridge_mode_valid().

Note that this function changes the behavior of this driver: previously,
in case of unknown formats, it would (wrongly) assume that it should
account for a 24-bits format - now it will return an error and refuse
to set clocks and/or enable the DSI.

This is done because setting the wrong data rate will only produce a
garbage output that the display will misinterpret both because this
driver doesn't actually provide any extra-spec format support and/or
because the data rate (hence, the HS clock) will be wrong.

Reviewed-by: Alexandre Mergnat <amerg...@baylibre.com>
Signed-off-by: AngeloGioacchino Del Regno 
<angelogioacchino.delre...@collabora.com>
---
 drivers/gpu/drm/mediatek/mtk_dsi.c | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c 
b/drivers/gpu/drm/mediatek/mtk_dsi.c
index b644505de98a..9501f4019199 100644
--- a/drivers/gpu/drm/mediatek/mtk_dsi.c
+++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
@@ -598,19 +598,12 @@ static int mtk_dsi_poweron(struct mtk_dsi *dsi)
        if (++dsi->refcount != 1)
                return 0;
 
-       switch (dsi->format) {
-       case MIPI_DSI_FMT_RGB565:
-               bit_per_pixel = 16;
-               break;
-       case MIPI_DSI_FMT_RGB666_PACKED:
-               bit_per_pixel = 18;
-               break;
-       case MIPI_DSI_FMT_RGB666:
-       case MIPI_DSI_FMT_RGB888:
-       default:
-               bit_per_pixel = 24;
-               break;
+       ret = mipi_dsi_pixel_format_to_bpp(dsi->format);
+       if (ret < 0) {
+               dev_err(dev, "Unknown MIPI DSI format %d\n", dsi->format);
+               return ret;
        }
+       bit_per_pixel = ret;
 
        dsi->data_rate = DIV_ROUND_UP_ULL(dsi->vm.pixelclock * bit_per_pixel,
                                          dsi->lanes);
@@ -793,12 +786,11 @@ mtk_dsi_bridge_mode_valid(struct drm_bridge *bridge,
                          const struct drm_display_mode *mode)
 {
        struct mtk_dsi *dsi = bridge_to_dsi(bridge);
-       u32 bpp;
+       int bpp;
 
-       if (dsi->format == MIPI_DSI_FMT_RGB565)
-               bpp = 16;
-       else
-               bpp = 24;
+       bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
+       if (bpp < 0)
+               return MODE_ERROR;
 
        if (mode->clock * bpp / dsi->lanes > 1500000)
                return MODE_CLOCK_HIGH;
-- 
2.43.0