linux-kernel - Re: [PATCH v1] scsi: libsas: set data_dir as DMA

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Date:   Mon, 31 Aug 2020 15:29:49 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     Luo Jiaxing <luojiaxing@...wei.com>, <martin.petersen@...cle.com>,
        <jejb@...ux.ibm.com>
CC:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <john.garry@...wei.com>, <chenxiang66@...ilicon.com>,
        <linuxarm@...wei.com>
Subject: Re: [PATCH v1] scsi: libsas: set data_dir as DMA_NONE if libata mark
 qc as NODATA


在 2020/8/26 15:24, Luo Jiaxing 写道:
> We found that it will fail every time when set feature to SATA disk by
> "sdparm -s WCE=0 /dev/sde".
> 
> After checking protocol, we know that MODE SELECT is the SCSI command for
> setting WCE, and it do not exist in the SATA protocol. Therefore, this
> commands are encapsulated in the SET FEATURE command in SATA protocol.
> The difference is that the MODE SELECT command sent to SAS disk contains
> data and is sent through the DMA. But when send to SATA disk through
> SET FEATURE command, it does not contain data.
> 
> I think libsas was not thorough enough in dealing with the situation, at
> sas_ata_qc_issue(), task->dma_dir is inherited from qc->dma_dir(qc->dma_dir
> is also inherited from SCSI). However, in ATA driver, if qc->tf.protocol is
> set to ATA_PROT_NODATA, ata_sg_setup() will not invoked by ata_qc_issue().
> It mean that ATA didn't use dma_dir and it's not reliable. So, if libsas
> still inherits from qc->dma_dir when there is no data need to be send. As a
> result, task with no data are mistakenly considered as carrying data and it
> will make LLDD report an error on IO completion.
> 
> So, When ATA driver mark tf->protocol as NODATA, dma_dir should be set as
> DMA_NONE. And we can see WCE is successfully disable for SATA disk then.
> 
> Euler:~ # sdparm -s WCE=0 /dev/sde
>       /dev/sde: ATA       ST4000NM0035-1V4  TN03
> Euler:~ # sdparm /dev/sde
>       /dev/sde: ATA       ST4000NM0035-1V4  TN03
> Read write error recovery mode page:
>     AWRE        1  [cha: n, def:  1]
>     ARRE        0  [cha: n, def:  0]
>     PER         0  [cha: n, def:  0]
> Caching (SBC) mode page:
>     WCE         0  [cha: y, def:  0]
>     RCD         0  [cha: n, def:  0]
> Control mode page:
>     SWP         0  [cha: n, def:  0]
> 
> Fixes: fa1c1e8f1ece ("[SCSI] Add SATA support to libsas")
> 
> Signed-off-by: Luo Jiaxing <luojiaxing@...wei.com>
> Reviewed-by: John Garry <john.garry@...wei.com>
> ---
>   drivers/scsi/libsas/sas_ata.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/libsas/sas_ata.c b/drivers/scsi/libsas/sas_ata.c
> index 6a521ba..a488798 100644
> --- a/drivers/scsi/libsas/sas_ata.c
> +++ b/drivers/scsi/libsas/sas_ata.c
> @@ -209,7 +209,10 @@ static unsigned int sas_ata_qc_issue(struct ata_queued_cmd *qc)
>   		task->num_scatter = si;
>   	}
>   
> -	task->data_dir = qc->dma_dir;
> +	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;
> 

Reviewed-by: Jason Yan <yanaijie@...wei.com>