lkml.org 
[lkml]   [2020]   [Sep]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v5 3/3] media: i2c: imx274: Add IMX274 power on and off sequence
Hello,

On Fri, Sep 04, 2020 at 10:04:10AM -0700, Sowjanya Komatineni wrote:
>
> On 9/4/20 1:55 AM, Jacopo Mondi wrote:
> > > > usleep_range() allows you to provide an interval in which your timeout
> > > > can be coalesced with others. Giving a [1usec, 2usec] range kind of
> > > > defeat the purpose. And most than everything, does sleeping for 2usec
> > > > serve any real purpose ?
> > > Following delay recommendation from DS for power on sequence.
> > >
> > 2 useconds ? Seems very short:)
> >
> As per IMX274 datasheet for power on sequence, 100ns is the min wait time
> after the last power supply of 1v8/1v2/2v8 is ON before releasing RESET
> high.

ook.. well, it's actually reasonable, it's just the time for the
regulators to ramp up, I initially thought it was the time for the
chip to exit reset.

Let me be a bit more picky and ask if you have considered busy waiting
on such a small sleep interval by using udelay. Again, as this happens
at chip power on only, the impact on the system of mis-using
usleep_range() is negligible, but according to documentation:

SLEEPING FOR "A FEW" USECS ( < ~10us? ):
* Use udelay

- Why not usleep?
On slower systems, (embedded, OR perhaps a speed-
stepped PC!) the overhead of setting up the hrtimers
for usleep *may* not be worth it. Such an evaluation
will obviously depend on your specific situation, but
it is something to be aware of.

Up to you, really!

Thanks
j

\
 
 \ /
  Last update: 2020-09-07 09:45    [W:0.070 / U:1.968 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site