Re: [PATCH] mmc: meson-gx: check for scatterlist size alignment in block mode

[Heiner Kallweit <hkallweit1@gmail.com>]

Am 18.12.2020 um 08:53 schrieb Dmitry Lebed:
> Enable SGDMA support for SD_IO_RW_EXTENDED and add proper check
> for scatterlist size alignment in block mode.
> 
> According to documentation, in SDIO block mode meson-gx DMA could
> only handle buffers with sizes that are multiples of SDIO block size.
> 
> Some SDIO drivers like brcmfmac use scatterlist API, but do not enforce
> proper scatterlist buffer size alignemnt, this looks like a root cause
> of non-working CMD53.
> 
It's been too long ago that I worked on this to provide real feedback.
Just one comment: Your commit description sounds like there's a problem
in drivers like brcmfmac. Wouldn't it be better then to first fix these
drivers?

> Some minor style fixes.
> 
> Signed-off-by: Dmitry Lebed <lebed.dmitry@gmail.com>
> ---
>  drivers/mmc/host/meson-gx-mmc.c | 37 ++++++++++++++++++++-------------
>  1 file changed, 22 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
> index 13f6a2c0ed04..eb6c02bc4a02 100644
> --- a/drivers/mmc/host/meson-gx-mmc.c
> +++ b/drivers/mmc/host/meson-gx-mmc.c
> @@ -227,7 +227,6 @@ static void meson_mmc_get_transfer_mode(struct mmc_host *mmc,
>  	struct mmc_data *data = mrq->data;
>  	struct scatterlist *sg;
>  	int i;
> -	bool use_desc_chain_mode = true;
>  
>  	/*
>  	 * When Controller DMA cannot directly access DDR memory, disable
> @@ -237,25 +236,33 @@ static void meson_mmc_get_transfer_mode(struct mmc_host *mmc,
>  	if (host->dram_access_quirk)
>  		return;
>  
> -	/*
> -	 * Broken SDIO with AP6255-based WiFi on Khadas VIM Pro has been
> -	 * reported. For some strange reason this occurs in descriptor
> -	 * chain mode only. So let's fall back to bounce buffer mode
> -	 * for command SD_IO_RW_EXTENDED.
> -	 */
> -	if (mrq->cmd->opcode == SD_IO_RW_EXTENDED)
> -		return;
> +	if (data->blocks > 1) {
> +		/*
> +		 * In block mode DMA descriptor format, "length" field indicates
> +		 * number of blocks and there is no way to pass DMA size that
> +		 * is not multiple of SDIO block size, making it impossible to
> +		 * tie more than one memory buffer with single SDIO block.
> +		 * Block mode sg buffer size should be aligned with SDIO block
> +		 * size, otherwise chain mode could not be used.
> +		 */
> +		for_each_sg(data->sg, sg, data->sg_len, i) {
> +			if (sg->length % data->blksz) {
> +				WARN_ONCE(1, "unaligned sg len %u blksize %u\n",
> +					  sg->length, data->blksz);
> +				return;
> +			}
> +		}
> +	}
>  
> -	for_each_sg(data->sg, sg, data->sg_len, i)
> +	for_each_sg(data->sg, sg, data->sg_len, i) {
>  		/* check for 8 byte alignment */
> -		if (sg->offset & 7) {
> +		if (sg->offset % 8) {
>  			WARN_ONCE(1, "unaligned scatterlist buffer\n");
> -			use_desc_chain_mode = false;
> -			break;
> +			return;
>  		}
> +	}
>  
> -	if (use_desc_chain_mode)
> -		data->host_cookie |= SD_EMMC_DESC_CHAIN_MODE;
> +	data->host_cookie |= SD_EMMC_DESC_CHAIN_MODE;
>  }
>  
>  static inline bool meson_mmc_desc_chain_mode(const struct mmc_data *data)
> 


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