linux-kernel - Re: [PATCH 2/3] drm/msm/dp: Shrink locking area of dp_aux

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Date:   Mon, 24 May 2021 09:22:43 -0700
From:   khsieh@...eaurora.org
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Rob Clark <robdclark@...il.com>, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        aravindh@...eaurora.org, Sean Paul <sean@...rly.run>
Subject: Re: [PATCH 2/3] drm/msm/dp: Shrink locking area of dp_aux_transfer()

On 2021-05-07 14:25, Stephen Boyd wrote:
> We don't need to hold the lock to inspect the message we're going to
> transfer, and we don't need to clear the busy flag either. Take the 
> lock
> later and bail out earlier if conditions aren't met.
> 
> Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Cc: Abhinav Kumar <abhinavk@...eaurora.org>
> Cc: Kuogee Hsieh <khsieh@...eaurora.org>
> Cc: aravindh@...eaurora.org
> Cc: Sean Paul <sean@...rly.run>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>

Reviewed-by: Kuogee Hsieh <khsieh@...eaurora.org>
> ---
>  drivers/gpu/drm/msm/dp/dp_aux.c | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c 
> b/drivers/gpu/drm/msm/dp/dp_aux.c
> index 91188466cece..b49810396513 100644
> --- a/drivers/gpu/drm/msm/dp/dp_aux.c
> +++ b/drivers/gpu/drm/msm/dp/dp_aux.c
> @@ -329,30 +329,29 @@ static ssize_t dp_aux_transfer(struct drm_dp_aux 
> *dp_aux,
>  	ssize_t ret;
>  	int const aux_cmd_native_max = 16;
>  	int const aux_cmd_i2c_max = 128;
> -	struct dp_aux_private *aux = container_of(dp_aux,
> -		struct dp_aux_private, dp_aux);
> +	struct dp_aux_private *aux;
> 
> -	mutex_lock(&aux->mutex);
> +	aux = container_of(dp_aux, struct dp_aux_private, dp_aux);
> 
>  	aux->native = msg->request & (DP_AUX_NATIVE_WRITE & 
> DP_AUX_NATIVE_READ);
> 
>  	/* Ignore address only message */
> -	if ((msg->size == 0) || (msg->buffer == NULL)) {
> +	if (msg->size == 0 || !msg->buffer) {
>  		msg->reply = aux->native ?
>  			DP_AUX_NATIVE_REPLY_ACK : DP_AUX_I2C_REPLY_ACK;
> -		ret = msg->size;
> -		goto unlock_exit;
> +		return msg->size;
>  	}
> 
>  	/* msg sanity check */
> -	if ((aux->native && (msg->size > aux_cmd_native_max)) ||
> -		(msg->size > aux_cmd_i2c_max)) {
> +	if ((aux->native && msg->size > aux_cmd_native_max) ||
> +	    msg->size > aux_cmd_i2c_max) {
>  		DRM_ERROR("%s: invalid msg: size(%zu), request(%x)\n",
>  			__func__, msg->size, msg->request);
> -		ret = -EINVAL;
> -		goto unlock_exit;
> +		return -EINVAL;
>  	}
> 
> +	mutex_lock(&aux->mutex);
> +
>  	dp_aux_update_offset_and_segment(aux, msg);
>  	dp_aux_transfer_helper(aux, msg, true);