linux-kernel - Re: [PATCHv3 1/2] mmc: block: Remove error check of hw

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Message-ID: <65d813c6-65c0-fb5b-2709-8068e1dc89c1@intel.com>
Date:   Tue, 11 Oct 2022 13:15:12 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Christian Löhle <CLoehle@...erstone.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv3 1/2] mmc: block: Remove error check of hw_reset on reset

On 10/10/22 17:03, Christian Löhle wrote:
> Before switching back to the right partition in mmc_blk_reset
> there used to be a check if hw_reset was even supported.
> This return value was removed, so there is no reason to check.
> Furthermore ensure part_curr is not falsely set to a valid value
> on reset or partition switch error.
> 
> Fixes: fefdd3c91e0a ("mmc: core: Drop superfluous validations in mmc_hw|sw_reset()")
> Cc: stable@...r.kernel.org
> 
> Signed-off-by: Christian Loehle <cloehle@...erstone.com>
> ---
> -v3: Ensure invalid part_curr on error
> -v2: Do not attempt to switch partitions if reset failed
> 
>  drivers/mmc/core/block.c | 29 ++++++++++++++---------------
>  1 file changed, 14 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index ce89611a136e..45a44edcc31a 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -134,6 +134,7 @@ struct mmc_blk_data {
>  	 * track of the current selected device partition.
>  	 */
>  	unsigned int	part_curr;
> +#define MMC_BLK_PART_INVALID	UINT_MAX	/* Unknown partition active */
>  	int	area_type;
>  
>  	/* debugfs files (only in main mmc_blk_data) */
> @@ -991,29 +992,27 @@ static int mmc_blk_reset(struct mmc_blk_data *md, struct mmc_host *host,
>  			 int type)
>  {
>  	int err;
> +	struct mmc_blk_data *main_md = dev_get_drvdata(&host->card->dev);
> +	int part_err;
>  
>  	if (md->reset_done & type)
>  		return -EEXIST;
>  
>  	md->reset_done |= type;
> +	main_md->part_curr = MMC_BLK_PART_INVALID;

This forces a partition switch even if it is not necessary.

>  	err = mmc_hw_reset(host->card);

This would be better:

	/*
	 * A successful reset will leave the card in the main partition, but
	 * upon failure it might not be, so set it to MMC_BLK_PART_INVALID
	 * in that case.
	 */
	main_md->part_curr = err ? MMC_BLK_PART_INVALID : main_md->part_type;

> +	if (err)
> +		return err;

There was a time when mmc requests would be retried directly without
going back through the block layer.  I don't think that can happen
anymore after a failed reset.  However, if you are going to skip the
partition switch, the commit message needs to explain that you have
checked the code paths and we never retry a request directly after a
failed reset.  Also a comment is needed to say the same.

>  	/* Ensure we switch back to the correct partition */
> -	if (err) {
> -		struct mmc_blk_data *main_md =
> -			dev_get_drvdata(&host->card->dev);
> -		int part_err;
> -
> -		main_md->part_curr = main_md->part_type;
> -		part_err = mmc_blk_part_switch(host->card, md->part_type);
> -		if (part_err) {
> -			/*
> -			 * We have failed to get back into the correct
> -			 * partition, so we need to abort the whole request.
> -			 */
> -			return -ENODEV;
> -		}
> +	part_err = mmc_blk_part_switch(host->card, md->part_type);
> +	if (part_err) {

Don't really need part_err. i.e. could be 

	if (mmc_blk_part_switch(host->card, md->part_type) {

> +		/*
> +		 * We have failed to get back into the correct
> +		 * partition, so we need to abort the whole request.
> +		 */
> +		return -ENODEV;
>  	}
> -	return err;
> +	return 0;
>  }
>  
>  static inline void mmc_blk_reset_success(struct mmc_blk_data *md, int type)