[Linux-stm32] [PATCH] drm/stm: dsi: compute LP <=> HS time delay

[Philippe CORNU]

Hi Antonio,

I suggest this new commit name to avoid special chars ("<=>")
drm/stm: dsi: compute time delays between LP and HS



On 5/31/21 5:48 PM, Antonio Borneo wrote:
> The driver uses a conservative set of hardcoded values for the
> time delay between LP and HS, for either data and clock lanes.
> 
> By using the info in STM32MP15x datasheet, compute the actual
> delay from lane's bps.
> For the other devices whose datasheet don't provide this info yet,
> stick to the legacy values.
> 
> Signed-off-by: Antonio Borneo <antonio.borneo at foss.st.com>
> ---
> To: Philippe CORNU <philippe.cornu at foss.st.com>
> To: Yannick Fertre <yannick.fertre at foss.st.com>
> To: Raphael GALLAIS-POU <raphael.gallais-pou at foss.st.com>
> Cc: linux-stm32 at st-md-mailman.stormreply.com
> 
> Ticket: https://intbugzilla.st.com/show_bug.cgi?id=91708
> 
>   drivers/gpu/drm/stm/dw_mipi_dsi-stm.c | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c b/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> index 8399d337589d..cd5054bb5bc1 100644
> --- a/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> +++ b/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> @@ -309,10 +309,31 @@ dw_mipi_dsi_get_lane_mbps(void *priv_data, const struct drm_display_mode *mode,
>   	return 0;
>   }
>   
> +#define DSI_PHY_DELAY(fp, vp, mbps) DIV_ROUND_UP((fp) * (mbps) + 1000 * (vp), 8000)
> +
>   static int
>   dw_mipi_dsi_phy_get_timing(void *priv_data, unsigned int lane_mbps,
>   			   struct dw_mipi_dsi_dphy_timing *timing)
>   {
> +	struct dw_mipi_dsi_stm *dsi = priv_data;
> +
> +	if (dsi->hw_version == HWVER_131) {
> +		/*
> +		 * From datasheet of STM32MP15x
> +		 * phy_clkhs2lp_time = (232+136*UI)/(8*UI)
> +		 * phy_clklp2hs_time = (512+40*UI)/(8*UI)
> +		 * phy_hs2lp_time = (128+64*UI)/(8*UI)
> +		 * phy_lp2hs_time = (256+32*UI)/(8*UI)
> +		 */
> +		timing->clk_hs2lp = DSI_PHY_DELAY(232, 136, lane_mbps);
> +		timing->clk_lp2hs = DSI_PHY_DELAY(512, 40, lane_mbps);
> +		timing->data_hs2lp = DSI_PHY_DELAY(128, 64, lane_mbps);
> +		timing->data_lp2hs = DSI_PHY_DELAY(256, 32, lane_mbps);
> +
> +		return 0;

I suggest to move "return 0" (and add an else) at the end of the 
function for readability.

> +	}
> +
> +	/* No data for the older DSI, yet */
>   	timing->clk_hs2lp = 0x40;
>   	timing->clk_lp2hs = 0x40;
>   	timing->data_hs2lp = 0x40;
> 

Computations look correct.

Thanks
Philippe