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Subject: Re: [PATCH v2] scsi: libsas: Reset num_scatter if libata mark qc as
 NODATA
To:     Jolly Shah <jollys@google.com>, <jejb@linux.ibm.com>,
        <martin.petersen@oracle.com>, <john.garry@huawei.com>,
        <a.darwish@linutronix.de>, <luojiaxing@huawei.com>,
        <dan.carpenter@oracle.com>, <b.zolnierkie@samsung.com>
CC:     <linux-scsi@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20210318225632.2481291-1-jollys@google.com>
From:   Jason Yan <yanaijie@huawei.com>
Message-ID: <5e7ea537-86ab-f654-1df4-765364116e18@huawei.com>
Date:   Fri, 19 Mar 2021 09:43:20 +0800
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在 2021/3/19 6:56, Jolly Shah 写道:
> When the cache_type for the scsi device is changed, the scsi layer
> issues a MODE_SELECT command. The caching mode details are communicated
> via a request buffer associated with the scsi command with data
> direction set as DMA_TO_DEVICE (scsi_mode_select). When this command
> reaches the libata layer, as a part of generic initial setup, libata
> layer sets up the scatterlist for the command using the scsi command
> (ata_scsi_qc_new). This command is then translated by the libata layer
> into ATA_CMD_SET_FEATURES (ata_scsi_mode_select_xlat). The libata layer
> treats this as a non data command (ata_mselect_caching), since it only
> needs an ata taskfile to pass the caching on/off information to the
> device. It does not need the scatterlist that has been setup, so it does
> not perform dma_map_sg on the scatterlist (ata_qc_issue). Unfortunately,
> when this command reaches the libsas layer(sas_ata_qc_issue), libsas
> layer sees it as a non data command with a scatterlist. It cannot
> extract the correct dma length, since the scatterlist has not been
> mapped with dma_map_sg for a DMA operation. When this partially
> constructed SAS task reaches pm80xx LLDD, it results in below warning.
> 
> "pm80xx_chip_sata_req 6058: The sg list address
> start_addr=0x0000000000000000 data_len=0x0end_addr_high=0xffffffff
> end_addr_low=0xffffffff has crossed 4G boundary"
> 
> This patch updates code to handle ata non data commands separately so
> num_scatter and total_xfer_len remain 0.
> 
> Fixes: 53de092f47ff ("scsi: libsas: Set data_dir as DMA_NONE if libata marks qc as NODATA")
> Signed-off-by: Jolly Shah <jollys@google.com>
> ---
> v2:
> - reorganized code to avoid setting num_scatter twice
> 
>   drivers/scsi/libsas/sas_ata.c | 9 ++++-----
>   1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/scsi/libsas/sas_ata.c b/drivers/scsi/libsas/sas_ata.c
> index 024e5a550759..8b9a39077dba 100644
> --- a/drivers/scsi/libsas/sas_ata.c
> +++ b/drivers/scsi/libsas/sas_ata.c
> @@ -201,18 +201,17 @@ static unsigned int sas_ata_qc_issue(struct ata_queued_cmd *qc)
>   		memcpy(task->ata_task.atapi_packet, qc->cdb, qc->dev->cdb_len);
>   		task->total_xfer_len = qc->nbytes;
>   		task->num_scatter = qc->n_elem;
> +		task->data_dir = qc->dma_dir;
> +	} else if (qc->tf.protocol == ATA_PROT_NODATA) {
> +		task->data_dir = DMA_NONE;

Hi Jolly & John,

We only set DMA_NONE for ATA_PROT_NODATA, I'm curious about why 
ATA_PROT_NCQ_NODATA and ATAPI_PROT_NODATA do not need to set DMA_NONE?

Thanks,
Jason


>   	} else {
>   		for_each_sg(qc->sg, sg, qc->n_elem, si)
>   			xfer += sg_dma_len(sg);
>   
>   		task->total_xfer_len = xfer;
>   		task->num_scatter = si;
> -	}
> -
> -	if (qc->tf.protocol == ATA_PROT_NODATA)
> -		task->data_dir = DMA_NONE;
> -	else
>   		task->data_dir = qc->dma_dir;
> +	}
>   	task->scatter = qc->sg;
>   	task->ata_task.retry_count = 1;
>   	task->task_state_flags = SAS_TASK_STATE_PENDING;
>