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. Daniel -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
