On Wed, Jun 18, 2014 at 11:36:43AM +0200, Daniel Mack wrote: > On 06/18/2014 11:32 AM, David Laight wrote: > > From: Of Daniel Mack > >> Sent: 18 June 2014 10:28 > >> To: balbi@xxxxxx; george.cherian@xxxxxx; bigeasy@xxxxxxxxxxxxx > >> Cc: sebastian.reimers@xxxxxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx; Daniel Mack > >> Subject: [PATCH 2/2] usb: musb: cppi41: fire hrtimer according to programmed channel length > >> > >> The musb/cppi41 code installs a hrtimer to work around DMA completion > >> interrupts that have fired too early on AM335x hardware. This timer > >> is currently programmed to first fire 140 nanoseconds after the DMA > >> completion callback. According to the commit which introduced it > >> (a655f481d83, "usb: musb: musb_cppi41: handle pre-mature TX complete > >> interrupt"), that value is is considered a 'rule of thumb' that worked > >> well with the test case described in the commit log. > >> > >> Test show, however, that for USB audio devices and much smaller packet > >> sizes, the timer has to fire earlier in order to correctly handle the audio > >> stream. The original test case had output transfer sizes of 1514 bytes, and > >> a delay of 140 nanoseconds. For audio devices with 24 bytes channel size, 3 > >> nanoseconds seem to work well. > > > > You can't really mean nanoseconds? > > Microseconds of course. Thanks for the heads-up. Fixed locally. Are you sending another one or want me to fix the commit log when applying here ? -- balbi
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