Subject: [PATCH v6 9/9] drm/mediatek: dsi: Use mipi_dsi_pixel_format_to_bpp() helper function

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 <[email protected]>
Signed-off-by: AngeloGioacchino Del Regno <[email protected]>
---
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



2024-02-15 09:29:17

by CK Hu (胡俊光)

[permalink] [raw]
Subject: Re: [PATCH v6 9/9] drm/mediatek: dsi: Use mipi_dsi_pixel_format_to_bpp() helper function

Hi, Angelo:

On Thu, 2024-02-15 at 09:53 +0100, AngeloGioacchino Del Regno wrote:
> 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: CK Hu <[email protected]>

>
> Reviewed-by: Alexandre Mergnat <[email protected]>
> Signed-off-by: AngeloGioacchino Del Regno <
> [email protected]>
> ---
> 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;