Re: [PATCH 1/3] drm/panel: st7701: Fix AVCL calculation

[neil.armstrong@linaro.org]

On 08/12/2023 16:48, Chris Morgan wrote:
> From: Chris Morgan <macromorgan@hotmail.com>
> 
> The AVCL register, according to the datasheet, comes in increments
> of -0.2v between -4.4v (represented by 0x0) to -5.0v (represented
> by 0x3). The current calculation is done by adding the defined
> AVCL value in mV to -4400 and then dividing by 200 to get the register
> value. Unfortunately if I subtract -4400 from -4400 I get -8800, which
> divided by 200 gives me -44. If I instead subtract -4400 from -4400
> I get 0, which divided by 200 gives me 0. Based on the datasheet this
> is the expected register value.
> 
> Fixes: 83b7a8e7e88e ("drm/panel/panel-sitronix-st7701: Parametrize voltage and timing")
> 
> Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
> ---
>   drivers/gpu/drm/panel/panel-sitronix-st7701.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-sitronix-st7701.c b/drivers/gpu/drm/panel/panel-sitronix-st7701.c
> index 0459965e1b4f..036ac403ed21 100644
> --- a/drivers/gpu/drm/panel/panel-sitronix-st7701.c
> +++ b/drivers/gpu/drm/panel/panel-sitronix-st7701.c
> @@ -288,7 +288,7 @@ static void st7701_init_sequence(struct st7701 *st7701)
>   		   FIELD_PREP(DSI_CMD2_BK1_PWRCTRL2_AVDD_MASK,
>   			      DIV_ROUND_CLOSEST(desc->avdd_mv - 6200, 200)) |
>   		   FIELD_PREP(DSI_CMD2_BK1_PWRCTRL2_AVCL_MASK,
> -			      DIV_ROUND_CLOSEST(-4400 + desc->avcl_mv, 200)));
> +			      DIV_ROUND_CLOSEST(-4400 - desc->avcl_mv, 200)));
>   
>   	/* T2D = 0.2us * T2D[3:0] */
>   	ST7701_DSI(st7701, DSI_CMD2_BK1_SPD1,

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>