On Fri, Dec 04, 2020 at 08:44:17AM +0000, Sean Young wrote: > On Fri, Dec 04, 2020 at 12:42:15AM +0100, Lino Sanfilippo wrote: > > According to commit 11fc4edc4 rounding to the closest integer has been > > introduced > > to improve precision in case that the pwm controller is used by the > > pwm-ir-tx driver. > > I dont know how strong the requirement is to round down the period in > > apply(), but I > > can imagine that this may be a good reason to deviate from this rule. > > (CCing Sean Young who introduced DIV_ROUND_CLOSEST) > > There was a problem where the carrier is incorrect for some IR hardware > which uses a carrier of 455kHz. With periods that small, rounding errors > do really matter and rounding down might cause problems. > > A policy of rounding down the carrier is not the right thing to do > for pwm-ir-tx, and such a change will probably break pwm-ir-tx in some > edge cases.
Let me rephrase that. Changing the division to rounding down will exactly revert the fix I made in commit 11fc4edc483bea8bf0efa0cc726886d2342f6fa6. So in the case described in that commit, the requested frequency was 455kHz, but rounding down resulted in a frequency of 476kHz. That's totally broken and a bad idea. Sean
