Hi,
Sorry, my previous review didn't go through.
On Fri, Mar 22, 2024 at 11:47:31AM +0100, Sean Nyekjaer wrote:
> When using the DSI interface via DSI2LVDS bridge, it seems a bit harsh
> to reguire the requested and the actual px clock to be within
> 50Hz. A typical LVDS display requires the px clock to be within +-10%.
>
> In case for HDMI .5% tolerance is required.
>
> Fixes: e01356d18273 ("drm/stm: dsi: provide the implementation of mode_valid()")
> Signed-off-by: Sean Nyekjaer <sean@xxxxxxxxxx>
> ---
> drivers/gpu/drm/stm/dw_mipi_dsi-stm.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c b/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> index d5f8c923d7bc..97936b0ef702 100644
> --- a/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> +++ b/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> @@ -322,8 +322,6 @@ dw_mipi_dsi_phy_get_timing(void *priv_data, unsigned int lane_mbps,
> return 0;
> }
>
> -#define CLK_TOLERANCE_HZ 50
> -
> static enum drm_mode_status
> dw_mipi_dsi_stm_mode_valid(void *priv_data,
> const struct drm_display_mode *mode,
> @@ -375,9 +373,10 @@ dw_mipi_dsi_stm_mode_valid(void *priv_data,
> /*
> * Filter modes according to the clock value, particularly useful for
> * hdmi modes that require precise pixel clocks.
> + * Check that px_clock is within .5% tolerance.
> */
> - if (px_clock_hz < target_px_clock_hz - CLK_TOLERANCE_HZ ||
> - px_clock_hz > target_px_clock_hz + CLK_TOLERANCE_HZ)
> + if (px_clock_hz < mult_frac(target_px_clock_hz, 995, 1000) ||
> + px_clock_hz > mult_frac(target_px_clock_hz, 1005, 1000))
> return MODE_CLOCK_RANGE;
I wonder if it's not something that should be made into a helper. We
have a couple of drivers doing it already, so it might be worth creating
a function that checks for a given struct clk pointer and pixel clock if
it's within parameters.
Maxime
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