Re: [PATCH] hwmon: (aquacomputer_d5next) Add selective 200ms delay after sending ctrl report

[Aleksa Savic <savicaleksa83@gmail.com>]

On 2023-07-29 15:44:32 GMT+02:00, Guenter Roeck wrote:
> On 7/29/23 04:27, Aleksa Savic wrote:
>> Add a 200ms delay after sending a ctrl report to Quadro,
>> Octo, D5 Next and Aquaero to give them enough time to
>> process the request and save the data to memory. Otherwise,
>> under heavier userspace loads where multiple sysfs entries
>> are usually set in quick succession, a new ctrl report could
>> be requested from the device while it's still processing the
>> previous one and fail with -EPIPE.
>>
>> Reported by a user on Github [1] and tested by both of us.
>>
>> [1] https://github.com/aleksamagicka/aquacomputer_d5next-hwmon/issues/82
>>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Aleksa Savic <savicaleksa83@gmail.com>
>> ---
>>   drivers/hwmon/aquacomputer_d5next.c | 25 +++++++++++++++++++++++++
>>   1 file changed, 25 insertions(+)
>>
>> diff --git a/drivers/hwmon/aquacomputer_d5next.c b/drivers/hwmon/aquacomputer_d5next.c
>> index a997dbcb563f..9cb55d51185a 100644
>> --- a/drivers/hwmon/aquacomputer_d5next.c
>> +++ b/drivers/hwmon/aquacomputer_d5next.c
>> @@ -652,6 +652,31 @@ static int aqc_send_ctrl_data(struct aqc_data *priv)
>>       ret = hid_hw_raw_request(priv->hdev, priv->secondary_ctrl_report_id,
>>                    priv->secondary_ctrl_report, priv->secondary_ctrl_report_size,
>>                    HID_FEATURE_REPORT, HID_REQ_SET_REPORT);
>> +    if (ret < 0)
>> +        return ret;
>> +
>> +    /*
>> +     * Wait 200ms before returning to make sure that the device actually processed both reports
>> +     * and saved ctrl data to memory. Otherwise, an aqc_get_ctrl_data() call made shortly after
>> +     * may fail with -EPIPE because the device is still busy and can't provide data. This can
>> +     * happen when userspace tools, such as fancontrol or liquidctl, write to sysfs entries in
>> +     * quick succession.
>> +     *
>> +     * 200ms was found to be the sweet spot between fixing the issue and not significantly
>> +     * prolonging the call. Quadro, Octo, D5 Next and Aquaero are currently known to be
>> +     * affected.
>> +     */
>> +    switch (priv->kind) {
>> +    case quadro:
>> +    case octo:
>> +    case d5next:
>> +    case aquaero:
>> +        msleep(200);
>> +        break;
>> +    default:
>> +        break;
>> +    }
>> +
>>       return ret;
>>   }
>>   
> 
> This would force writes to sleep even if there is no subsequent operation.
> Please make this conditional by saving the most recent access time and wait
> on the subsequent operation. I would also suggest to store the wait time
> in struct aqc_data to avoid the switch statement in the data path. An example
> for a driver doing something similar is drivers/hwmon/pmbus/zl6100.c.
> 
> Thanks,
> Guenter
> 

Thanks, will take a look at it. Please ignore v2 of this patch in this case.

Aleksa