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

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Message-ID: <191698899544068194e28246454c2613.squirrel@www.codeaurora.org>
Date:	Sun, 25 Oct 2015 14:40:49 -0000
From:	ygardi@...eaurora.org
To:	"Akinobu Mita" <akinobu.mita@...il.com>
Cc:	"Yaniv Gardi" <ygardi@...eaurora.org>,
	"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

> 2015-09-02 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.

>
>>
>>         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
>> --
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>


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