Messages in this thread |  | | Subject | Re: [PATCH v5 3/3] media: i2c: imx274: Add IMX274 power on and off sequence | From | Sowjanya Komatineni <> | Date | Tue, 8 Sep 2020 11:13:17 -0700 |
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On 9/7/20 12:48 AM, Jacopo Mondi wrote: > 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 Thanks Jacopo. Will update in v6 to use udelay.
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