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

[Jerome Brunet <jbrunet@baylibre.com>]

On Fri 18 Dec 2020 at 10:08, Heiner Kallweit <hkallweit1@gmail.com> wrote:

> 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?

While this may be true, I think the proposed change is better than the
device/command specific work around we had so far.

>
>> Some minor style fixes.
>> 
>> Signed-off-by: Dmitry Lebed <lebed.dmitry@gmail.com>

Thx.

Reviewed-by: Jerome Brunet <jbrunet@baylibre.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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