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

From: Ian Arkver
Date: Tue Dec 13 2016 - 05:10:59 EST

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.