linux-kernel - Re: [PATCH 1/1] scsi: ufs: make sure all interrupts are processed

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Date:   Mon, 5 Feb 2018 10:27:02 +0530
From:   "Asutosh Das (asd)" <asutoshd@...eaurora.org>
To:     Avri Altman <Avri.Altman@....com>,
        "subhashj@...eaurora.org" <subhashj@...eaurora.org>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "vivek.gautam@...eaurora.org" <vivek.gautam@...eaurora.org>,
        "rnayak@...eaurora.org" <rnayak@...eaurora.org>,
        "vinholikatti@...il.com" <vinholikatti@...il.com>,
        "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        Venkat Gopalakrishnan <venkatg@...eaurora.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] scsi: ufs: make sure all interrupts are processed

On 2/2/2018 8:53 AM, Asutosh Das (asd) wrote:
> On 1/31/2018 1:09 PM, Avri Altman wrote:
>> Hi,
>> Can you elaborate how this can even happen?
>> Isn't the interrupt aggregation capability should attend for those cases?
>>
>> Thanks,
>> Avri
>>
>>> -----Original Message-----
>>> From: linux-scsi-owner@...r.kernel.org [mailto:linux-scsi-
>>> owner@...r.kernel.org] On Behalf Of Asutosh Das
>>> Sent: Tuesday, January 30, 2018 6:54 AM
>>> To: subhashj@...eaurora.org; cang@...eaurora.org;
>>> vivek.gautam@...eaurora.org; rnayak@...eaurora.org;
>>> vinholikatti@...il.com; jejb@...ux.vnet.ibm.com;
>>> martin.petersen@...cle.com
>>> Cc: linux-scsi@...r.kernel.org; Venkat Gopalakrishnan
>>> <venkatg@...eaurora.org>; Asutosh Das <asutoshd@...eaurora.org>; open
>>> list <linux-kernel@...r.kernel.org>
>>> Subject: [PATCH 1/1] scsi: ufs: make sure all interrupts are processed
>>>
>>> From: Venkat Gopalakrishnan <venkatg@...eaurora.org>
>>>
>>> As multiple requests are submitted to the ufs host controller in 
>>> parallel there
>>> could be instances where the command completion interrupt arrives 
>>> later for a
>>> request that is already processed earlier as the corresponding 
>>> doorbell was
>>> cleared when handling the previous interrupt. Read the interrupt 
>>> status in a
>>> loop after processing the received interrupt to catch such interrupts 
>>> and handle
>>> it.
>>>
>>> Signed-off-by: Venkat Gopalakrishnan <venkatg@...eaurora.org>
>>> Signed-off-by: Asutosh Das <asutoshd@...eaurora.org>
>>> ---
>>>   drivers/scsi/ufs/ufshcd.c | 27 +++++++++++++++++++--------
>>>   1 file changed, 19 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c index
>>> 8af2af3..58d81de 100644
>>> --- a/drivers/scsi/ufs/ufshcd.c
>>> +++ b/drivers/scsi/ufs/ufshcd.c
>>> @@ -5357,19 +5357,30 @@ static irqreturn_t ufshcd_intr(int irq, void 
>>> *__hba)
>>>       u32 intr_status, enabled_intr_status;
>>>       irqreturn_t retval = IRQ_NONE;
>>>       struct ufs_hba *hba = __hba;
>>> +    int retries = hba->nutrs;
>>>
>>>       spin_lock(hba->host->host_lock);
>>>       intr_status = ufshcd_readl(hba, REG_INTERRUPT_STATUS);
>>> -    enabled_intr_status =
>>> -        intr_status & ufshcd_readl(hba, REG_INTERRUPT_ENABLE);
>>>
>>> -    if (intr_status)
>>> -        ufshcd_writel(hba, intr_status, REG_INTERRUPT_STATUS);
>>> +    /*
>>> +     * There could be max of hba->nutrs reqs in flight and in worst 
>>> case
>>> +     * if the reqs get finished 1 by 1 after the interrupt status is
>>> +     * read, make sure we handle them by checking the interrupt status
>>> +     * again in a loop until we process all of the reqs before 
>>> returning.
>>> +     */
>>> +    do {
>>> +        enabled_intr_status =
>>> +            intr_status & ufshcd_readl(hba,
>>> REG_INTERRUPT_ENABLE);
>>> +        if (intr_status)
>>> +            ufshcd_writel(hba, intr_status,
>>> REG_INTERRUPT_STATUS);
>>> +        if (enabled_intr_status) {
>>> +            ufshcd_sl_intr(hba, enabled_intr_status);
>>> +            retval = IRQ_HANDLED;
>>> +        }
>>> +
>>> +        intr_status = ufshcd_readl(hba, REG_INTERRUPT_STATUS);
>>> +    } while (intr_status && --retries);
>>>
>>> -    if (enabled_intr_status) {
>>> -        ufshcd_sl_intr(hba, enabled_intr_status);
>>> -        retval = IRQ_HANDLED;
>>> -    }
>>>       spin_unlock(hba->host->host_lock);
>>>       return retval;
>>>   }
>>> -- 
>>> Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
>>> Inc.
>>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a 
>>> Linux
>>> Foundation Collaborative Project.
>>
> 
> Hi
> yes - interrupt aggregation makes sense here. But there were some 
> performance concerns with it; well, I don't have the data to back that 
> up now though.
> However, I can code it up and check it.
> Will post it in some time.
> 
> -asd
> 
Hi Avri,
I went through the UFS HCI - v2.1 spec. Specifically, in sec 7.2.3 it 
explicitly mentions that the software should determine if new TRs were 
completed since the interrupt status was last read/cleared. This step is 
independent of aggregation.

So I think the above implementation makes sense. Please let me know if I 
understood your concern correctly.

-asd

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a 
Linux Foundation Collaborative Project