Messages in this thread | | | Date | Thu, 18 Nov 2021 10:09:41 +0000 | From | "Russell King (Oracle)" <> | Subject | Re: [PATCH] pwm: Use div64_ul instead of do_div |
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On Wed, Nov 17, 2021 at 12:24:00PM +0100, Uwe Kleine-König wrote: > Hello, > > On Wed, Nov 17, 2021 at 02:04:26AM +0000, cgel.zte@gmail.com wrote: > > From: Changcheng Deng <deng.changcheng@zte.com.cn> > > > > do_div() does a 64-by-32 division. If the divisor is unsigned long, using > > div64_ul can avoid truncation to 32-bit. > > After some research I understood your commit log. I'd write: > > do_div() does a 64-by-32 division. Here the divsor is an > unsigned long which on some platforms is 64 bit wide. So use > div64_ul instead of do_div to avoid a possible truncation. > > The priority of this patch seems to be low, as the device seems to exist > only on (32bit) arm.
... where unsigned long is 32-bit.
In any case, for this to overflow, we would need to have a clock in excess of 2^32-1 Hz, or around 4GHz - and if we had such a situation on 32-bit devices, we need to change the type for holding the frequency in the clk API, and probably a lot of code in the CCF as well.
Unless there is a real reason for this change, I would suggest leaving the code as is - there is absolutely no point in making these divisions more expensive unless there is a real reason.
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