From: Jacopo Mondi <jacopo@jmondi.org>
To: Sowjanya Komatineni <skomatineni@nvidia.com>
Cc: thierry.reding@gmail.com, jonathanh@nvidia.com,
sakari.ailus@iki.fi, hverkuil@xs4all.nl,
jacopo+renesas@jmondi.org, luca@lucaceresoli.net,
leonl@leopardimaging.com, robh+dt@kernel.org,
lgirdwood@gmail.com, broonie@kernel.org,
linux-media@vger.kernel.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 3/3] media: i2c: imx274: Add IMX274 power on and off sequence
Date: Mon, 7 Sep 2020 09:48:54 +0200 [thread overview]
Message-ID: <20200907074854.uxq4a76k5amjfopi@uno.localdomain> (raw)
In-Reply-To: <5ebe8d22-86fb-7bf2-ab19-e729caf8d88f@nvidia.com>
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
next prev parent reply other threads:[~2020-09-07 7:45 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-02 2:04 [PATCH v5 0/3] IMX274 fixes and power on and off implementation Sowjanya Komatineni
2020-09-02 2:04 ` [PATCH v5 1/3] media: i2c: imx274: Fix Y_OUT_SIZE register setting Sowjanya Komatineni
2020-09-02 2:04 ` [PATCH v5 2/3] dt-bindings: media: imx274: Add optional input clock and supplies Sowjanya Komatineni
2020-09-02 6:46 ` Luca Ceresoli
2020-09-02 6:52 ` Luca Ceresoli
2020-09-03 12:55 ` Jacopo Mondi
2020-09-03 16:05 ` Sowjanya Komatineni
2020-09-03 16:35 ` Jacopo Mondi
2020-09-03 16:40 ` Sowjanya Komatineni
2020-09-08 9:33 ` Sakari Ailus
2020-09-08 14:34 ` Jacopo Mondi
2020-09-08 18:10 ` Sowjanya Komatineni
2020-09-02 2:04 ` [PATCH v5 3/3] media: i2c: imx274: Add IMX274 power on and off sequence Sowjanya Komatineni
2020-09-03 15:03 ` Jacopo Mondi
2020-09-03 16:25 ` Sowjanya Komatineni
2020-09-04 8:55 ` Jacopo Mondi
[not found] ` <5ebe8d22-86fb-7bf2-ab19-e729caf8d88f@nvidia.com>
2020-09-07 7:48 ` Jacopo Mondi [this message]
2020-09-08 18:13 ` Sowjanya Komatineni
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