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Date: Thu, 30 Jul 2020 10:54:32 +0200
From: Martin Kepplinger <martin.kepplinger@...i.sm>
To: James Bottomley <James.Bottomley@...senPartnership.com>,
Alan Stern <stern@...land.harvard.edu>
Cc: Bart Van Assche <bvanassche@....org>,
Can Guo <cang@...eaurora.org>, martin.petersen@...cle.com,
linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel@...i.sm
Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release
On 30.07.20 10:52, Martin Kepplinger wrote:
> On 29.07.20 20:29, James Bottomley wrote:
>> On Wed, 2020-07-29 at 14:25 -0400, Alan Stern wrote:
>>> On Wed, Jul 29, 2020 at 06:43:48PM +0200, Martin Kepplinger wrote:
>> [...]
>>>>>> --- a/drivers/scsi/scsi_error.c
>>>>>> +++ b/drivers/scsi/scsi_error.c
>>>>>> @@ -554,16 +554,8 @@ int scsi_check_sense(struct scsi_cmnd
>>>>>> *scmd)
>>>>>> * so that we can deal with it there.
>>>>>> */
>>>>>> if (scmd->device->expecting_cc_ua) {
>>>>>> - /*
>>>>>> - * Because some device does not queue
>>>>>> unit
>>>>>> - * attentions correctly, we carefully
>>>>>> check
>>>>>> - * additional sense code and qualifier
>>>>>> so as
>>>>>> - * not to squash media change unit
>>>>>> attention.
>>>>>> - */
>>>>>> - if (sshdr.asc != 0x28 || sshdr.ascq !=
>>>>>> 0x00)
>>>>>> {
>>>>>> - scmd->device->expecting_cc_ua =
>>>>>> 0;
>>>>>> - return NEEDS_RETRY;
>>>>>> - }
>>>>>> + scmd->device->expecting_cc_ua = 0;
>>>>>> + return NEEDS_RETRY;
>>>>>
>>>>> Well, yes, but you can't do this because it would lose us media
>>>>> change events in the non-suspend/resume case which we really
>>>>> don't want. That's why I was suggesting a new flag.
>>>>>
>>>>> James
>>>>
>>>> also if I set expecting_cc_ua in resume() only, like I did?
>>>
>>> That wouldn't make any difference. The information sent by your
>>> card reader has sshdr.asc == 0x28 and sshdr.ascq == 0x00 (you can see
>>> it in the log). So because of the code here in scsi_check_sense(),
>>> which you can't change, the Unit Attention sent by the card reader
>>> would not be retried even if you do set the flag in resume().
>>
>> But if we had a new flag, like expecting_media_change, you could set
>> that in resume and we could condition the above test in the code on it
>> and reset it and do a retry if it gets set. I'm not saying we have to
>> do it this way, but it sounds like we have to do something in the
>> kernel, so I think the flag will become necessary but there might be a
>> bit of policy based dance around how it gets set in the kernel (to
>> avoid losing accurate media change events).
>>
>> James
>>
>
> Maybe I should just start a new discussion with a patch, but the below
> is what makes sense to me (when I understand you correctly) and seems to
> work. I basically add a new flag, so that the old flags behave unchanged
> and only call it during *runtime* resume for SD cards:
>
>
> --- a/drivers/scsi/scsi_error.c
> +++ b/drivers/scsi/scsi_error.c
> @@ -553,15 +553,21 @@ int scsi_check_sense(struct scsi_cmnd *scmd)
> * information that we should pass up to the upper-level
> driver
> * so that we can deal with it there.
> */
> - if (scmd->device->expecting_cc_ua) {
> + if (scmd->device->expecting_cc_ua ||
> + scmd->device->expecting_media_change) {
> /*
> * Because some device does not queue unit
> * attentions correctly, we carefully check
> * additional sense code and qualifier so as
> - * not to squash media change unit attention.
> + * not to squash media change unit attention;
> + * unless expecting_media_change is set, indicating
> + * that the media (most likely) didn't change
> + * but a device only believes so (for example
> + * because of suspend/resume).
> */
> - if (sshdr.asc != 0x28 || sshdr.ascq != 0x00) {
> - scmd->device->expecting_cc_ua = 0;
> + if ((sshdr.asc != 0x28 || sshdr.ascq != 0x00) ||
> + scmd->device->expecting_media_change) {
> + scmd->device->expecting_media_change = 0;
oops, I missed expecting_cc_ua here, but you get the idea.
> return NEEDS_RETRY;
> }
> }
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index d90fefffe31b..b647fab2b663 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -114,6 +114,7 @@ static void sd_shutdown(struct device *);
> static int sd_suspend_system(struct device *);
> static int sd_suspend_runtime(struct device *);
> static int sd_resume(struct device *);
> +static int sd_resume_runtime(struct device *);
> static void sd_rescan(struct device *);
> static blk_status_t sd_init_command(struct scsi_cmnd *SCpnt);
> static void sd_uninit_command(struct scsi_cmnd *SCpnt);
> @@ -574,7 +575,7 @@ static const struct dev_pm_ops sd_pm_ops = {
> .poweroff = sd_suspend_system,
> .restore = sd_resume,
> .runtime_suspend = sd_suspend_runtime,
> - .runtime_resume = sd_resume,
> + .runtime_resume = sd_resume_runtime,
> };
>
> static struct scsi_driver sd_template = {
> @@ -3652,6 +3653,21 @@ static int sd_resume(struct device *dev)
> return ret;
> }
>
> +static int sd_resume_runtime(struct device *dev)
> +{
> + struct scsi_disk *sdkp = dev_get_drvdata(dev);
> +
> + /* Some SD cardreaders report media change when resuming from
> suspend
> + * because they can't keep track during suspend. */
> +
> + /* XXX This is not unproblematic though: We won't notice when a card
> + * was really changed during runtime suspend! We basically rely
> on users
> + * to unmount or suspend before doing so. */
> + sdkp->device->expecting_media_change = 1;
> +
> + return sd_resume(dev);
> +}
> +
> /**
> * init_sd - entry point for this driver (both when built in or when
> * a module).
> diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
> index bc5909033d13..8c8f053f71c8 100644
> --- a/include/scsi/scsi_device.h
> +++ b/include/scsi/scsi_device.h
> @@ -169,6 +169,8 @@ struct scsi_device {
> * this device */
> unsigned expecting_cc_ua:1; /* Expecting a CHECK_CONDITION/UNIT_ATTN
> * because we did a bus reset. */
> + unsigned expecting_media_change:1; /* Expecting media change
> ASC/ASCQ
> + when it actually doesn't
> change */
> unsigned use_10_for_rw:1; /* first try 10-byte read / write */
> unsigned use_10_for_ms:1; /* first try 10-byte mode sense/select */
> unsigned set_dbd_for_ms:1; /* Set "DBD" field in mode sense */
>
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