Re: [PATCH 1/2] media/rc/imon.c: make send_packet() delay configurable

Mauro Carvalho Chehab
2013-03-14T15:02:03Z

Em Sun, 24 Feb 2013 21:19:29 +0100
Kevin Baradon <kevin.baradon@gmail.com> escreveu:

> Some imon devices (like 15c2:0036) need a higher delay between send_packet calls.
> Default value is still 5ms to avoid regressions on already working hardware.
>
> Also use interruptible wait to avoid load average going too high (and let caller handle signals).
>
> Signed-off-by: Kevin Baradon <kevin.baradon@gmail.com>
> ---
> drivers/media/rc/imon.c | 14 +++++++++++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
> index 78d109b..a3e66a0 100644
> --- a/drivers/media/rc/imon.c
> +++ b/drivers/media/rc/imon.c
> @@ -347,6 +347,11 @@ module_param(pad_stabilize, int, S_IRUGO | S_IWUSR);
> MODULE_PARM_DESC(pad_stabilize, "Apply stabilization algorithm to iMON PAD "
> "presses in arrow key mode. 0=disable, 1=enable (default).");
>
> +static unsigned int send_packet_delay = 5;
> +module_param(send_packet_delay, uint, S_IRUGO | S_IWUSR);
> +MODULE_PARM_DESC(send_packet_delay, "Minimum delay between send_packet() calls "
> + "(default 5ms)");
> +

Users will find a hard time discovering what delay is needed for each device.

If this is a per-device type property, then it should, instead, be associated
with the device's USB ID.

The better would be to encapsulate it at the USB device table, like adding a
NEED_(extra)_DELAY flag, like:

{ USB_DEVICE(0x15c2, 0x0036), .driver_info = NEED_10MS_DELAY },

If such flag is zero (like on all devices where .driver_info is not filled, as
Kernel zeroes the memory on all static vars), then it will keep using 5ms.

Another alternative would be to use .driver_info for the device type, and
add a logic to handle different types with different logic. This is what
mceusb.c does, for example.

> /*
> * In certain use cases, mouse mode isn't really helpful, and could actually
> * cause confusion, so allow disabling it when the IR device is open.
> @@ -535,12 +540,15 @@ static int send_packet(struct imon_context *ictx)
> kfree(control_req);
>
> /*
> - * Induce a mandatory 5ms delay before returning, as otherwise,
> + * Induce a mandatory delay before returning, as otherwise,
> * send_packet can get called so rapidly as to overwhelm the device,
> * particularly on faster systems and/or those with quirky usb.
> + * Do not use TASK_UNINTERRUPTIBLE as this routine is called quite often
> + * and doing so will increase load average slightly. Caller will handle
> + * signals itself.
> */
> - timeout = msecs_to_jiffies(5);
> - set_current_state(TASK_UNINTERRUPTIBLE);
> + timeout = msecs_to_jiffies(send_packet_delay);
> + set_current_state(TASK_INTERRUPTIBLE);
> schedule_timeout(timeout);
>
> return retval;

Regards,
Mauro