linux-kernel - Re: [PATCH 1/2] pwm: mtk-disp: Disable shadow registers before setting backlight values

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Message-ID: <20230126150203.dnsbw2l2fzyg3oi5@notapiano>
Date:   Thu, 26 Jan 2023 10:06:50 -0500
From:   Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     thierry.reding@...il.com, u.kleine-koenig@...gutronix.de,
        matthias.bgg@...il.com, weiqing.kong@...iatek.com,
        jitao.shi@...iatek.com, linux-pwm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH 1/2] pwm: mtk-disp: Disable shadow registers before
 setting backlight values

On Mon, Jan 23, 2023 at 05:06:14PM +0100, AngeloGioacchino Del Regno wrote:
> If shadow registers usage is not desired, disable that before performing
> any write to CON0/1 registers in the .apply() callback, otherwise we may
> lose clkdiv or period/width updates.
> 
> Fixes: cd4b45ac449a ("pwm: Add MediaTek MT2701 display PWM driver support")
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>  drivers/pwm/pwm-mtk-disp.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-mtk-disp.c b/drivers/pwm/pwm-mtk-disp.c
> index 692a06121b28..82b430d881a2 100644
> --- a/drivers/pwm/pwm-mtk-disp.c
> +++ b/drivers/pwm/pwm-mtk-disp.c
> @@ -138,6 +138,19 @@ static int mtk_disp_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  	high_width = mul_u64_u64_div_u64(state->duty_cycle, rate, div);
>  	value = period | (high_width << PWM_HIGH_WIDTH_SHIFT);
>  
> +	if (mdp->data->bls_debug && !mdp->data->has_commit) {
> +		/*
> +		 * For MT2701, disable double buffer before writing register

Not necessarily part of this series, but I guess it would make sense to remove
the "For MT2701". It's no longer exclusive to that SoC and the condition in the
if above makes it clear when this happens.

Reviewed-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
Tested-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>

On MT8192 Asurada Spherion.

Thanks,
Nícolas

> +		 * and select manual mode and use PWM_PERIOD/PWM_HIGH_WIDTH.
> +		 */
> +		mtk_disp_pwm_update_bits(mdp, mdp->data->bls_debug,
> +					 mdp->data->bls_debug_mask,
> +					 mdp->data->bls_debug_mask);
> +		mtk_disp_pwm_update_bits(mdp, mdp->data->con0,
> +					 mdp->data->con0_sel,
> +					 mdp->data->con0_sel);
> +	}
> +
>  	mtk_disp_pwm_update_bits(mdp, mdp->data->con0,
>  				 PWM_CLKDIV_MASK,
>  				 clk_div << PWM_CLKDIV_SHIFT);
> @@ -152,17 +165,6 @@ static int mtk_disp_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  		mtk_disp_pwm_update_bits(mdp, mdp->data->commit,
>  					 mdp->data->commit_mask,
>  					 0x0);
> -	} else {
> -		/*
> -		 * For MT2701, disable double buffer before writing register
> -		 * and select manual mode and use PWM_PERIOD/PWM_HIGH_WIDTH.
> -		 */
> -		mtk_disp_pwm_update_bits(mdp, mdp->data->bls_debug,
> -					 mdp->data->bls_debug_mask,
> -					 mdp->data->bls_debug_mask);
> -		mtk_disp_pwm_update_bits(mdp, mdp->data->con0,
> -					 mdp->data->con0_sel,
> -					 mdp->data->con0_sel);
>  	}
>  
>  	mtk_disp_pwm_update_bits(mdp, DISP_PWM_EN, mdp->data->enable_mask,
> -- 
> 2.39.0
> 
>