Re: [PATCH RFC] [media] s5k6aa: set usleep_range greater 0

From: Sakari Ailus
Date: Tue Dec 13 2016 - 05:54:15 EST

On Tue, Dec 13, 2016 at 10:10:51AM +0000, Ian Arkver wrote:
> On 13/12/16 09:43, Sakari Ailus wrote:
> >Hi Nicholas,
> >
> >On Tue, Dec 13, 2016 at 02:58:02AM +0100, Nicholas Mc Guire wrote:
> >>As this is not in atomic context and it does not seem like a critical
> >>timing setting a range of 1ms allows the timer subsystem to optimize
> >>the hrtimer here.
> >I'd suggest not to. These delays are often directly visible to the user in
> >use cases where attention is indeed paid to milliseconds.
> >
> >The same applies to register accesses. An delay of 0 to 100 µs isn't much as
> >such, but when you multiply that with the number of accesses it begins to
> >add up.
> >
> Data sheet for this device [1] says STBYN deassertion to RSTN deassertion
> should be >50us, though this is actually referenced to MCLK startup. See
> Figure 36, Power-Up Sequence, page 42.
> I think the usleep range here could be greatly reduced and opened up to
> allow hr timer tweaks if desired.
> [1]

Good point. Datasheets do not always tell everything though; it'd be good to
get a comment from the original driver authors on why they've used the value
which can now be found in the driver.

Sakari Ailus
e-mail: sakari.ailus@xxxxxx XMPP: sailus@xxxxxxxxxxxxxx