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

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