Subject: Re: [PATCH] mmc: meson: Fix usage of meson_mmc_post_req()

From: Kevin Hilman <[email-masked]>
Date: Mon, 24 Jan 2022 14:05:17 -0800

Hello Rong,

First, thank you finding the issue and for submitting a fix!

Rong Chen <[email-masked]> writes:

> To ensure the DMA moves data correctly from memory to
> peripherals, DMA unmapping when the MMC request done
> with calls meson_mmc_post_req().
>
> Signed-off-by: Rong Chen <[email-masked]>

The patch looks correct, but I think I think the changelog could be
improved.  If I understand the code correctly, I think what you're doing
is:

"""
Currently meson_mmc_post_req() is called in meson_mmc_request() right
after _start_cmd().  This could lead to DMA unmapping before the request
is actually finished.

To fix, ton't call meson_mmc_post_req() until _request_done().
"""

Kevin

> ---
>  drivers/mmc/host/meson-gx-mmc.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
> index 8f36536cb1b6..6a9554ae4b1c 100644
> --- a/drivers/mmc/host/meson-gx-mmc.c
> +++ b/drivers/mmc/host/meson-gx-mmc.c
> @@ -173,6 +173,7 @@ struct meson_host {
>  	int irq;
>  
>  	bool vqmmc_enabled;
> +	bool needs_pre_post_req;
>  };
>  
>  #define CMD_CFG_LENGTH_MASK GENMASK(8, 0)
> @@ -663,6 +664,8 @@ static void meson_mmc_request_done(struct mmc_host *mmc,
>  	struct meson_host *host = mmc_priv(mmc);
>  
>  	host->cmd = NULL;
> +	if (host->needs_pre_post_req)
> +		meson_mmc_post_req(mmc, mrq, 0);
>  	mmc_request_done(host->mmc, mrq);
>  }
>  
> @@ -880,7 +883,7 @@ static int meson_mmc_validate_dram_access(struct mmc_host *mmc, struct mmc_data
>  static void meson_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
>  {
>  	struct meson_host *host = mmc_priv(mmc);
> -	bool needs_pre_post_req = mrq->data &&
> +	host->needs_pre_post_req = mrq->data &&
>  			!(mrq->data->host_cookie & SD_EMMC_PRE_REQ_DONE);
>  
>  	/*
> @@ -896,22 +899,19 @@ static void meson_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
>  		}
>  	}
>  
> -	if (needs_pre_post_req) {
> +	if (host->needs_pre_post_req) {
>  		meson_mmc_get_transfer_mode(mmc, mrq);
>  		if (!meson_mmc_desc_chain_mode(mrq->data))
> -			needs_pre_post_req = false;
> +			host->needs_pre_post_req = false;
>  	}
>  
> -	if (needs_pre_post_req)
> +	if (host->needs_pre_post_req)
>  		meson_mmc_pre_req(mmc, mrq);
>  
>  	/* Stop execution */
>  	writel(0, host->regs + SD_EMMC_START);
>  
>  	meson_mmc_start_cmd(mmc, mrq->sbc ?: mrq->cmd);
> -
> -	if (needs_pre_post_req)
> -		meson_mmc_post_req(mmc, mrq, 0);
>  }
>  
>  static void meson_mmc_read_resp(struct mmc_host *mmc, struct mmc_command *cmd)
>
> base-commit: 356f3f2c5756bbb67a515760966a40fc7043cdda
> -- 
> 2.25.1

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