linux-kernel - Re: [PATCH v3 13/15] scsi: ufs: add missing memory barriers

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Date:	Mon, 26 Oct 2015 21:23:17 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	Yaniv Gardi <ygardi@...eaurora.org>
Cc:	Rob Herring <robherring2@...il.com>,
	Jej B <james.bottomley@...senpartnership.com>,
	Paul Bolle <pebolle@...cali.nl>,
	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	linux-arm-msm@...r.kernel.org, Santosh Y <santoshsy@...il.com>,
	linux-scsi-owner@...r.kernel.org,
	Subhash Jadavani <subhashj@...eaurora.org>,
	Gilad Broner <gbroner@...eaurora.org>,
	Dolev Raviv <draviv@...eaurora.org>,
	Vinayak Holikatti <vinholikatti@...il.com>,
	"James E.J. Bottomley" <jbottomley@...n.com>
Subject: Re: [PATCH v3 13/15] scsi: ufs: add missing memory barriers

2015-10-25 23:40 GMT+09:00  <ygardi@...eaurora.org>:
>> 2015-09-02 19:13 GMT+09:00 Yaniv Gardi <ygardi@...eaurora.org>:
>>> Performing several writes to UFS host controller registers has
>>> no gurrantee of ordering, so we must make sure register writes
>>> to setup request list base address etc. are performed before the
>>> run/stop register is enabled.
>>> In addition, when setting up a task request, we must make sure
>>> the updating of descriptors takes places before ringing the
>>> doorbell, similarly to setting up a transfer request.
>>>
>>> Signed-off-by: Gilad Broner <gbroner@...eaurora.org>
>>> Signed-off-by: Yaniv Gardi <ygardi@...eaurora.org>
>>>
>>> ---
>>>  drivers/scsi/ufs/ufshcd.c | 21 +++++++++++++++------
>>>  1 file changed, 15 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>>> index fc2a52d..298511a 100644
>>> --- a/drivers/scsi/ufs/ufshcd.c
>>> +++ b/drivers/scsi/ufs/ufshcd.c
>>> @@ -401,11 +401,9 @@ static inline int ufshcd_get_lists_status(u32 reg)
>>>          *  1           UTRLRDY
>>>          *  2           UTMRLRDY
>>>          *  3           UCRDY
>>> -        *  4           HEI
>>> -        *  5           DEI
>>> -        * 6-7          reserved
>>> +        * 4-7          reserved
>>>          */
>>> -       return (((reg) & (0xFF)) >> 1) ^ (0x07);
>>> +       return ((reg & 0xFF) >> 1) ^ 0x07;
>>>  }
>>>
>>>  /**
>>> @@ -2726,7 +2724,7 @@ out:
>>>   * To bring UFS host controller to operational state,
>>>   * 1. Enable required interrupts
>>>   * 2. Configure interrupt aggregation
>>> - * 3. Program UTRL and UTMRL base addres
>>> + * 3. Program UTRL and UTMRL base address
>>>   * 4. Configure run-stop-registers
>>>   *
>>>   * Returns 0 on success, non-zero value on failure
>>> @@ -2756,8 +2754,13 @@ static int ufshcd_make_hba_operational(struct
>>> ufs_hba *hba)
>>>                         REG_UTP_TASK_REQ_LIST_BASE_H);
>>>
>>>         /*
>>> +        * Make sure base address and interrupt setup are updated before
>>> +        * enabling the run/stop registers below.
>>> +        */
>>> +       wmb();
>>> +
>>> +       /*
>>>          * UCRDY, UTMRLDY and UTRLRDY bits must be 1
>>> -        * DEI, HEI bits must be 0
>>>          */
>>>         reg = ufshcd_readl(hba, REG_CONTROLLER_STATUS);
>>>         if (!(ufshcd_get_lists_status(reg))) {
>>> @@ -3920,7 +3923,13 @@ static int ufshcd_issue_tm_cmd(struct ufs_hba
>>> *hba, int lun_id, int task_id,
>>>
>>>         /* send command to the controller */
>>>         __set_bit(free_slot, &hba->outstanding_tasks);
>>> +
>>> +       /* Make sure descriptors are ready before ringing the task
>>> doorbell */
>>> +       wmb();
>>> +
>>>         ufshcd_writel(hba, 1 << free_slot, REG_UTP_TASK_REQ_DOOR_BELL);
>>> +       /* Make sure that doorbell is committed immediately */
>>> +       wmb();
>>
>> Is this wmb() after ringing tm doorbell is needed?
>
> Well, Mita, in the case of DB register (Request DB and TASK DB), every
> write operation to the DB should be barrier, as if not, out of order
> writing to this register might cause inconsistency in its value, and thus,
> un-handled requests/tasks.

I couldn't fully understand why out of order writing to TASK DB
register causes inconsistency.
In the TASK request completion (ufshcd_tmc_handler), TASK DB register
is read before handling finished requests, so it ensures that all
write operations for TASK DB have been performed.

>>
>>>
>>>         spin_unlock_irqrestore(host->host_lock, flags);
>>>
>>> --
>>> 1.8.5.2
>>>
>>> --
>>> QUALCOMM ISRAEL, on behalf of Qualcomm Innovation Center, Inc. is a
>>> member of Code Aurora Forum, hosted by The Linux Foundation
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
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>>
>
>
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