RE: [PATCH 4/5] scsi: ufs: rework link start-up process

[Seungwon Jeon <tgih.jun@samsung.com>]

On Tuesday, April 30, 2013, Sujit Reddy Thumma wrote:
> On 4/30/2013 12:03 PM, Seungwon Jeon wrote:
> > On Monday, April 29, 2013, Sujit Reddy Thumma wrote:
> >> On 4/29/2013 3:54 PM, Seungwon Jeon wrote:
> >>> On Monday, April 29, 2013, Sujit Reddy Thumma wrote:
> >>>> On 4/26/2013 10:44 AM, Seungwon Jeon wrote:
> >>>>> On Thursday, April 25, 2013 , Sujit Reddy Thumma wrote:
> >>>>>> On 4/24/2013 9:36 PM, Seungwon Jeon wrote:
> >>>>>>> Link start-up requires long time with multiphase handshakes
> >>>>>>> between UFS host and device. This affects driver's probe time.
> >>>>>>> This patch let link start-up run asynchronously.
> >>>>>>> And completion time of uic command is defined to avoid a
> >>>>>>> permanent wait.
> >>>>>>
> >>>>>> I have similar patch posted few days back "scsi: ufs: Generalize UFS
> >>>>>> Interconnect Layer (UIC) command support" which does a bit more (mutex,
> >>>>>> error handling) than what is done here. Can that be used/improved?
> >>>>> I completed to check your patch to compare it now.
> >>>>> Though it's just my thought, the patch I sent is more intuitive on the whole.
> >>>>> Considering other dme operations which I have introduced, it looks like matched.
> >>>>
> >>>> There are lot of code duplications you might want to minimize building a
> >>>> DME command.
> >>>>
> >>>>> Of course, you may disagree.
> >>>>> But I think the part of mutex is needed. It's a good point.
> >>>>> In case of error handling, I didn't catch nothing special.
> >>>>> Rather, handling link lost case is not proper.
> >>>>> When ufs host meets link lost status, it should start with dme_reset not retried dme_linkstartup.
> >>>>
> >>>> In section 7.2.1 (Host Controller Initialization) of JESD223A UFS HCI
> >>>> v1.1  specification I find this -
> >>>>
> >>>> 6. Sent DME_LINKSTARTUP command to start the link startup procedure
> >>>> 9. Check value of HCS.DP and make sure that there is a device attached
> >>>> to the Link. If presence of a device is detected, go to step 10;
> >>>> otherwise, resend the DME_LINKSTARTUP command after IS.ULLS has been set
> >>>> to 1 (Go to step 6). IS.ULLS equal 1 indicates that the UFS Device is
> >>>> ready for a link startup.
> >>>>
> >>>> Going by the spec. just retrying with DME_LINKSTARTUP is correct.
> >>> Yes, as you quoted above, HCI standard mentions that.
> >>> Also, the following is mentioned.
> >>> UIC Link Lost Status (ULLS) corresponds to the UniPro DME_LINKLOST.ind
> >>> I just referred unipro specification.
> >>> When DME_LINKLOST.ind is generated, this affects the Link is put in the LinkLost state.
> >>> Unipro spec says that DME User must apply a DME_RESET to redo the boot sequence.
> >>> If there is misunderstood meaning and I have something to miss, we can discuss more.
> >>> Please let me know.
> >>
> >> Yes, it looks like the two specs. are conflicting each other. I guess we
> >> need to take this to Jedec for clarification. Meanwhile, to be on safe
> >> side can we add a retry mechanism that does ufshcd_hba_enable() before
> >> sending DME_LINKSTARTUP again? This way we can be sure that the
> >> DME_RESET and DME_ENABLE is taken care by the host reset itself.
> > Yes, If the latter case is applied, 'ufshcd_hba_enable' will be start entry for retry.
> > Further, IS.ULLS could be handled through the interrupt instead of polling for retry mechanism?
> 
> Agree, but the interrupt handling will be tailored for two things - 1)
> bootup case where scsi_scan_host is not yet called. 2) the case where
> link lost occurred after a long time after bootup where there is no need
> to do scsi_scan_host again.
Yes, it could be another patch.

> 
> >
> >>
> >>>
> >>>>
> >>>> In addition, it doesn't say what happens if IS.ULLS never sets to 1.
> >>>> Probably, the case which never happens.
> >>>>
> >>>>> And it would be good if link start-up procedure is done in separate process, not in driver probe.
> >>>> True.
> >>>>
> >>>>> If it's all right with you, I'd like to update lock mechanism for uic command.
> >>>>> I can add your signed-off. Please let me know your opinion.
> >>>> I would like to get a third opinion as both the patches needs modifications.
> >>>>
> >>>> Some comments below:
> >>>>
> >>>>>>
> >>>>>>>
> >>>>>>> Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
> >>>>>>> ---
> >>>>>>>      drivers/scsi/ufs/ufshcd.c |  114 +++++++++++++++++++++++++++++++++-----------
> >>>>>>>      drivers/scsi/ufs/ufshcd.h |    6 ++-
> >>>>>>>      2 files changed, 89 insertions(+), 31 deletions(-)
> >>>>>>>
> >>>>>>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> >>>>>>> index efe2256..76ff332 100644
> >>>>>>> --- a/drivers/scsi/ufs/ufshcd.c
> >>>>>>> +++ b/drivers/scsi/ufs/ufshcd.c
> >>>>>>> @@ -38,6 +38,7 @@
> >>>>>>>      #define UFSHCD_ENABLE_INTRS	(UTP_TRANSFER_REQ_COMPL |\
> >>>>>>>      				 UTP_TASK_REQ_COMPL |\
> >>>>>>>      				 UFSHCD_ERROR_MASK)
> >>>>>>> +#define UIC_CMD_TIMEOUT	100
> >>>>>>>
> >>>>>>>      enum {
> >>>>>>>      	UFSHCD_MAX_CHANNEL	= 0,
> >>>>>>> @@ -357,13 +358,15 @@ static inline void ufshcd_hba_capabilities(struct ufs_hba *hba)
> >>>>>>>      }
> >>>>>>>
> >>>>>>>      /**
> >>>>>>> - * ufshcd_send_uic_command - Send UIC commands to unipro layers
> >>>>>>> + * ufshcd_dispatch_uic_cmd - Dispatch UIC commands to unipro layers
> >>>>>>>       * @hba: per adapter instance
> >>>>>>>       * @uic_command: UIC command
> >>>>>>>       */
> >>>>>>>      static inline void
> >>>>>>> -ufshcd_send_uic_command(struct ufs_hba *hba, struct uic_command *uic_cmnd)
> >>>>>>> +ufshcd_dispatch_uic_cmd(struct ufs_hba *hba, struct uic_command *uic_cmnd)
> >>>>>>>      {
> >>>>>>> +	init_completion(&uic_cmnd->done);
> >>>>>>> +
> >>>>>>>      	/* Write Args */
> >>>>>>>      	ufshcd_writel(hba, REG_UIC_COMMAND_ARG_1, uic_cmnd->argument1);
> >>>>>>>      	ufshcd_writel(hba, REG_UIC_COMMAND_ARG_2, uic_cmnd->argument2);
> >>>>>>> @@ -375,6 +378,45 @@ ufshcd_send_uic_command(struct ufs_hba *hba, struct uic_command *uic_cmnd)
> >>>>>>>      }
> >>>>>>>
> >>>>>>>      /**
> >>>>>>> + * ufshcd_wait_for_uic_cmd - Wait complectioin of UIC command
> >>>>>>> + * @hba: per adapter instance
> >>>>>>> + * @uic_command: UIC command
> >>>>>>> + *
> >>>>>>> + * Returns 0 only if success.
> >>>>>>> + */
> >>>>>>> +static int ufshcd_wait_for_uic_cmd(struct ufs_hba *hba)
> >>>>>>> +{
> >>>>>>> +	struct uic_command *uic_cmd = &hba->active_uic_cmd;
> >>>>>>> +	int ret;
> >>>>>>> +
> >>>>>>> +	if (wait_for_completion_timeout(&uic_cmd->done,
> >>>>>>> +					msecs_to_jiffies(UIC_CMD_TIMEOUT)))
> >>>>>>> +		ret = ufshcd_get_uic_cmd_result(hba);
> >>>>>>> +	else
> >>>>>>> +		ret = -ETIMEDOUT;
> >>>>>>> +
> >>>>>>> +	return ret;
> >>>>>>> +}
> >>>>>>> +
> >>>>>>> +/**
> >>>>>>> + * ufshcd_ready_uic_cmd - Check if controller is ready
> >>>>>>> + *                        to accept UIC commands
> >>>>>>> + * @hba: per adapter instance
> >>>>>>> + * Return true on success, else false
> >>>>>>> + */
> >>>>>>> +static inline bool ufshcd_ready_uic_cmd(struct ufs_hba *hba)
> >>>>>>> +{
> >>>>>>> +	if (ufshcd_readl(hba, REG_CONTROLLER_STATUS) & UIC_COMMAND_READY) {
> >>>>>>> +		return true;
> >>>>>>> +	} else {
> >>>>>>> +		dev_err(hba->dev,
> >>>>>>> +				"Controller not ready"
> >>>>>>> +				" to accept UIC commands\n");
> >>>>>>> +		return false;
> >>>>>>> +	}
> >>>>>>> +}
> >>>>>>> +
> >>>>>>> +/**
> >>>>>>>       * ufshcd_map_sg - Map scatter-gather list to prdt
> >>>>>>>       * @lrbp - pointer to local reference block
> >>>>>>>       *
> >>>>>>> @@ -735,15 +777,10 @@ static int ufshcd_dme_link_startup(struct ufs_hba *hba)
> >>>>>>>      {
> >>>>>>>      	struct uic_command *uic_cmd;
> >>>>>>>      	unsigned long flags;
> >>>>>>> +	int ret;
> >>>>>>>
> >>>>>>> -	/* check if controller is ready to accept UIC commands */
> >>>>>>> -	if (((ufshcd_readl(hba, REG_CONTROLLER_STATUS)) &
> >>>>>>> -	    UIC_COMMAND_READY) == 0x0) {
> >>>>>>> -		dev_err(hba->dev,
> >>>>>>> -			"Controller not ready"
> >>>>>>> -			" to accept UIC commands\n");
> >>>>>>> +	if (!ufshcd_ready_uic_cmd(hba))
> >>>>>>>      		return -EIO;
> >>>>>>> -	}
> >>>>>>>
> >>>>>>>      	spin_lock_irqsave(hba->host->host_lock, flags);
> >>>>>>>
> >>>>>>> @@ -754,13 +791,16 @@ static int ufshcd_dme_link_startup(struct ufs_hba *hba)
> >>>>>>>      	uic_cmd->argument2 = 0;
> >>>>>>>      	uic_cmd->argument3 = 0;
> >>>>>>>
> >>>>>>> -	/* enable UIC related interrupts */
> >>>>>>> -	ufshcd_enable_intr(hba, UIC_COMMAND_COMPL);
> >>>>>>> +	/* Dispatching UIC commands to controller */
> >>>>>>> +	ufshcd_dispatch_uic_cmd(hba, uic_cmd);
> >>>>>>>
> >>>>>>> -	/* sending UIC commands to controller */
> >>>>>>> -	ufshcd_send_uic_command(hba, uic_cmd);
> >>>>>>>      	spin_unlock_irqrestore(hba->host->host_lock, flags);
> >>>>>>> -	return 0;
> >>>>>>> +
> >>>>>>> +	ret = ufshcd_wait_for_uic_cmd(hba);
> >>>>
> >>>> Error code is incorrect. only -ETIMEDOUT is valid others are just DME
> >>>> errors.
> >>> Only success returns '0', other positive value from dme and -ETIMEDOUT mean failure.
> >>> Error code can be reused purely, not being redefined.
> >>> I am seeing that -EINVAL represents from 01h to 07h in your handling.
> >>> It looks like error's detail is disappear. Exact return might be needed from DME.
> >> okay.
> >>
> >>>
> >>>>
> >>>> Also, spec. clearly mentions a retry mechanism which means that there
> >>>> could be some timing issues anticipated where the UIC layer cannot
> >>>> respond properly.
> >>> Sorry, I didn't catch your meaning fully. Where can I refer to it?
> >>
> >> I meant the same retry mechanism mentioned in the section 7.2.1 (Host
> >> Controller Initialization) of JESD223A UFS HCI v1.1.
> >>
> >>>
> >>>>
> >>>>
> >>>>>>> +	if (ret)
> >>>>>>> +		dev_err(hba->dev, "link startup: error code %d returned\n", ret);
> >>>>>>> +
> >>>>>>> +	return ret;
> >>>>>>>      }
> >>>>>>>
> >>>>>>>      /**
> >>>>>>> @@ -898,6 +938,9 @@ static int ufshcd_initialize_hba(struct ufs_hba *hba)
> >>>>>>>      	if (ufshcd_hba_enable(hba))
> >>>>>>>      		return -EIO;
> >>>>>>>
> >>>>>>> +	/* enable UIC related interrupts */
> >>>>>>> +	ufshcd_enable_intr(hba, UIC_COMMAND_COMPL | UIC_ERROR);
> >>>>
> >>>> The recovery when UIC_ERROR happens is broken because of re-entrancy to
> >>>> dme_link_startup from ufshcd_fatal_err_handler(). So better handle with
> >>>> timeout than allowing controller to raise a UIC_ERROR until that is fixed?
> >>> I also recognize error handling should be done further.
> >>> Ok, I agree with you.
> >>>
> >>>>
> >>>>>>> +
> >>>>>>>      	/* Configure UTRL and UTMRL base address registers */
> >>>>>>>      	ufshcd_writel(hba, REG_UTP_TRANSFER_REQ_LIST_BASE_L,
> >>>>>>>      		      lower_32_bits(hba->utrdl_dma_addr));
> >>>>>>> @@ -909,7 +952,9 @@ static int ufshcd_initialize_hba(struct ufs_hba *hba)
> >>>>>>>      		      upper_32_bits(hba->utmrdl_dma_addr));
> >>>>>>>
> >>>>>>>      	/* Initialize unipro link startup procedure */
> >>>>>>> -	return ufshcd_dme_link_startup(hba);
> >>>>>>> +	schedule_work(&hba->link_startup_wq);
> >>>>>>> +
> >>>>>>> +	return 0;
> >>>>>>>      }
> >>>>>>>
> >>>>>>>      /**
> >>>>>>> @@ -1186,6 +1231,16 @@ ufshcd_transfer_rsp_status(struct ufs_hba *hba, struct ufshcd_lrb *lrbp)
> >>>>>>>      }
> >>>>>>>
> >>>>>>>      /**
> >>>>>>> + * ufshcd_uic_cmd_compl - handle completion of uic command
> >>>>>>> + * @hba: per adapter instance
> >>>>>>> + */
> >>>>>>> +static void ufshcd_uic_cmd_compl(struct ufs_hba *hba, u32 intr_status)
> >>>>>>> +{
> >>>>>>> +	if (intr_status & UIC_COMMAND_COMPL)
> >>>>
> >>>> why this redundant check if it is already checked in ufshcd_sl_intr()?
> >>> Yes, it's currently not needed.
> >>> It will be used to identify several uic command. ([PATCH 5/5] scsi: ufs: add dme operations)
> >>> Anyway, it's better to be removed here.
> >>>
> >>>>
> >>>>>>> +		complete(&hba->active_uic_cmd.done);
> >>>>>>> +}
> >>>>>>> +
> >>>>>>> +/**
> >>>>>>>       * ufshcd_transfer_req_compl - handle SCSI and query command completion
> >>>>>>>       * @hba: per adapter instance
> >>>>>>>       */
> >>>>>>> @@ -1225,25 +1280,26 @@ static void ufshcd_transfer_req_compl(struct ufs_hba *hba)
> >>>>>>>      }
> >>>>>>>
> >>>>>>>      /**
> >>>>>>> - * ufshcd_uic_cc_handler - handle UIC command completion
> >>>>>>> + * ufshcd_link_startup - link initialization
> >>>>>>>       * @work: pointer to a work queue structure
> >>>>>>> - *
> >>>>>>> - * Returns 0 on success, non-zero value on failure
> >>>>>>>       */
> >>>>>>> -static void ufshcd_uic_cc_handler (struct work_struct *work)
> >>>>>>> +static void ufshcd_link_startup(struct work_struct *work)
> >>>>>>>      {
> >>>>>>>      	struct ufs_hba *hba;
> >>>>>>> +	int ret;
> >>>>>>>
> >>>>>>> -	hba = container_of(work, struct ufs_hba, uic_workq);
> >>>>>>> +	hba = container_of(work, struct ufs_hba, link_startup_wq);
> >>>>>>>
> >>>>>>> -	if ((hba->active_uic_cmd.command == UIC_CMD_DME_LINK_STARTUP) &&
> >>>>>>> -	    !(ufshcd_get_uic_cmd_result(hba))) {
> >>>>>>> +	ret = ufshcd_dme_link_startup(hba);
> >>>>>>> +	if (ret)
> >>>>>>> +		goto out;
> >>>>>>>
> >>>>>>> -		if (ufshcd_make_hba_operational(hba))
> >>>>>>> -			dev_err(hba->dev,
> >>>>>>> -				"cc: hba not operational state\n");
> >>>>>>> -		return;
> >>>>>>> -	}
> >>>>>>> +	ret = ufshcd_make_hba_operational(hba);
> >>>>>>> +	if (ret)
> >>>>>>> +		goto out;
> >>>>>>> +	return;
> >>>>>>> +out:
> >>>>>>> +	dev_err(hba->dev, "link startup failed %d\n", ret);
> >>>>>>>      }
> >>>>>>>
> >>>>>>>      /**
> >>>>>>> @@ -1307,7 +1363,7 @@ static void ufshcd_sl_intr(struct ufs_hba *hba, u32 intr_status)
> >>>>>>>      		ufshcd_err_handler(hba);
> >>>>>>>
> >>>>>>>      	if (intr_status & UIC_COMMAND_COMPL)
> >>>>>>> -		schedule_work(&hba->uic_workq);
> >>>>>>> +		ufshcd_uic_cmd_compl(hba, intr_status);
> >>>>>>>
> >>>>>>>      	if (intr_status & UTP_TASK_REQ_COMPL)
> >>>>>>>      		ufshcd_tmc_handler(hba);
> >>>>>>> @@ -1694,7 +1750,7 @@ int ufshcd_init(struct device *dev, struct ufs_hba **hba_handle,
> >>>>>>>      	init_waitqueue_head(&hba->ufshcd_tm_wait_queue);
> >>>>>>>
> >>>>>>>      	/* Initialize work queues */
> >>>>>>> -	INIT_WORK(&hba->uic_workq, ufshcd_uic_cc_handler);
> >>>>>>> +	INIT_WORK(&hba->link_startup_wq, ufshcd_link_startup);
> >>>>
> >>>> Can we use async function calls kernel/async.c instead of having work
> >>>> queues as this is only used during boot up?
> >>> As we know, both probe and resume are sensitive to execution time.
> >>> I guess link startup procedure will also be activated in driver's resume.
> >>> Do you have any specific reason for async function?
> >>>
> >>
> >> I guess most UFS devices currently are embedded and have rootfs on them.
> >> If we use schedule_work there is no synchronization mechanism to check
> >> whether the device link startup is completed and device is available for
> >> the userspace to mount the partitions. Having async mechanism in place,
> >> the prepare_namespace() does wait for such async probes to be completed
> >> before mounting the rootfs.
> > I understand your meaning.
> > If you are considering that, I think 'scsi_scan_host' has a role for that.
> > 'scsi_scan_host' will be the conclusion and be done in async subsystem.
> > 'scsi_scan_host' is actually called, after finishing link startup procedure.
> 
> with this patch the scsi_scan_host() is called after the work is
> scheduled. Which means that link_startup_wq might be scheduled after
> prepare_namespace().
AFAIK, the work is scheduled immediately. So I think we don't need to worry about that.
I guess you want to gather all of initialization sequence into async mechanism including link startup.
If your intention is for that reason, it's okay to use async_schedule.
Then, we may reuse these in driver's resume.
I should have answered quickly, but I have a day off yesterday.
If you have any opinion, please let me know.

Thanks,
Seungwon Jeon
> 
> >
> >>
> >> I agree that the resume is sensitive to execute time but during resume
> >> you can't schedule link startup work because the fs/block/scsi layer
> >> expects the device availability as soon as resume operation is
> >> completed. So ufshcd_link_startup() should be called in the resume
> >> context itself or implement a synchronization mechanism like blocking
> >> scsi layer queuing requests until link startup is completed.
> > 'scsi_block_requests' and  'scsi_unblock_requests' can be used during suspend/resume.
> > After the link startup is finished and host is ready, 'scsi_unblock_requests' will be called.
> >
> > Thanks,
> > Seungwon Jeon
> >>
> >> Would following implementation looks better?
> >>
> >>
> >> ufshcd_async_probe()
> >> {
> >> ...
> >>     ufshcd_link_startup(hba);
> >> ...
> >> }
> >>
> >> ufshcd_resume()
> >> {
> >> ...
> >> ufshcd_link_startup(hba);
> >> ...
> >> }
> >>
> >> ufshcd_init()
> >> {
> >> ...
> >> async_schedule(ufshcd_async_probe, hba);
> >> ...
> >> }
> >>
> >>
> >> --
> 
> --
> Regards,
> Sujit
> --
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