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

Seungwon Jeon
2013-04-30T06:33:53Z

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?

>
> >
> >>
> >> 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.

>
> 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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