linux-kernel - Re: [PATCH v2] ata: libata-scsi: Fix get identity data failed

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Message-ID: <087b77f8-3ff2-87ce-d197-e238b8ad9047@kernel.org>
Date:   Mon, 8 May 2023 00:02:59 +0900
From:   Damien Le Moal <dlemoal@...nel.org>
To:     John Garry <john.g.garry@...cle.com>,
        yangxingui <yangxingui@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, prime.zeng@...ilicon.com,
        kangfenglong@...wei.com
Subject: Re: [PATCH v2] ata: libata-scsi: Fix get identity data failed

On 2023/05/05 18:51, John Garry wrote:
> On 05/05/2023 10:14, yangxingui wrote:
>>> hmmm... is it really acceptable that libata is referencing libsas? I 
>>> didn't think that it would be. libsas uses libata, not the other way 
>>> around.
>> Yeah, I didn't expect that either. Is there any other way? If so, is 
>> patch v1 OK?
> 
> I still think that we can do better than v1.
> 
>>>
>>>>>   #include <linux/libata.h>
>>>>>   #include <linux/hdreg.h>
>>>>>   #include <linux/uaccess.h>
>>>>> @@ -2745,10 +2746,17 @@ static struct ata_device 
>>>>> *__ata_scsi_find_dev(struct ata_port *ap,
>>>>>    *    Associated ATA device, or %NULL if not found.
>>>>>    */
>>>>>   struct ata_device *
>>>>> -ata_scsi_find_dev(struct ata_port *ap, const struct scsi_device 
>>>>> *scsidev)
>>>> Why drop the const ?
>>>>
>>>>> +ata_scsi_find_dev(struct ata_port *ap, struct scsi_device *scsidev)
>>>>>   {
>>>>> -    struct ata_device *dev = __ata_scsi_find_dev(ap, scsidev);
>>>>> +    struct ata_device *dev;
>>>>> +
>>>>> +    if (ap->flags & ATA_FLAG_SAS_HOST) {
>>>
>>> And this is SAS host. Not necessarily libsas (even though with ipr 
>>> libata usage gone, it would be the only user).
>> Add a new flag only for libsas?
> 
> No, because of previous reason.
> 
> Please remind me - at what point do we error within ata_scsi_find_dev() 
> and return NULL for a libsas host?
> 
> Note: it would be good to include that commit message for future reference.
> 
> Maybe we could add a method to ata_port_operations to do this lookup. I 
> assume that is abusing ata_port_operations purpose, since it's mostly 
> for HW methods.
> 
> Or do we actually use sdev->hostdata for libata or libsas? If not, maybe 
> we could store the struct ata_device pointer there.
> 
> I'm just thinking out loud now...

Agree. Ideally, libasas should not be any different than a for a drive used with
ahci/sata/pata adapters. After all, all of them are scsi devices as well. So we
need to understand why this happens only with libsas and correct the device
setup there.

-- 
Damien Le Moal
Western Digital Research