Re: [PATCH] ALSA: usb-audio: fix incorrect clock source setting
From: chihhao chen <hidden>
Date: 2021-07-26 08:42:21
Also in:
alsa-devel, linux-mediatek, lkml
Hello, Attach USB descriptor of clock source and selectior for this earphone. AC Clock Source Descriptor: ------------------------------ Value Valuename 0x08 bLength 0x24 bDescriptorType 0x0A bDescriptorSubtype 0x09 bClockID 0x03 bmAttributes 0x07 bmControls 0x00 bAssocTerminal 0x00 iClockSource Hex dump: 0x08 0x24 0x0A 0x09 0x03 0x07 0x00 0x00 AC Clock Selector Descriptor: ------------------------------ Value Valuename 0x09 bLength 0x24 bDescriptorType 0x0B bDescriptorSubtype 0x0B bClockID 0x02 bNrInPins 0x09 baCSourceID(1) 0x0A baCSourceID(2) 0x03 bmControls 0x00 iClockSelector Hex dump: 0x09 0x24 0x0B 0x0B 0x02 0x09 0x0A 0x03 0x00 AC Clock Source Descriptor: ------------------------------ Value Valuename 0x08 bLength 0x24 bDescriptorType 0x0A bDescriptorSubtype 0x0A bClockID 0x03 bmAttributes 0x07 bmControls 0x00 bAssocTerminal 0x00 iClockSource Hex dump: 0x08 0x24 0x0A 0x0A 0x03 0x07 0x00 0x00 AC Clock Selector Descriptor: ------------------------------ Value Valuename 0x09 bLength 0x24 bDescriptorType 0x0B bDescriptorSubtype 0x0C bClockID 0x02 bNrInPins 0x09 baCSourceID(1) 0x0A baCSourceID(2) 0x03 bmControls 0x00 iClockSelector Hex dump: 0x09 0x24 0x0B 0x0C 0x02 0x09 0x0A 0x03 0x00 Thanks Chihhao On Mon, 2021-07-26 at 02:16 +0000, Geraldo Nascimento wrote:
On Sun, Jul 25, 2021 at 7:44 AM Takashi Iwai [off-list ref] wrote:quoted
On Sat, 24 Jul 2021 17:04:13 +0200, Geraldo Nascimento wrote:quoted
On Sat, Jul 24, 2021 at 8:05 AM Takashi Iwai [off-list ref] wrote:quoted
This looks like a regression introduced by the recent commit d2e8f641257d ("ALSA: usb-audio: Explicitly set up the clock selector"), which is a fix for certain devices. Too bad that the behavior really depends on the device...Dr. Iwai, perhaps we could restrict the generalized fix for the Behringer UFX1604 / UFX1204 with some simple logic to devices that only have *one* clock source. In that case the clock selector must be set to the only clock source. This way we keep the generalization without breaking devices with more than one clock source. Just an idea.I don't think it's easy to generalize. All those bugs are more or less BIOS bugs, and a logic doesn't apply always, just because it's a bug :) For example, setting the clock selector itself should be a valid operation from the specification POV, while this leads to breakage on some devices. So, even if we add a more generic workaround, we need to see which side effect is more commonly seen at first. TakashiHello, Like I said in one of the other emails in this thread, it's hard to pinpoint a cause for the breakage of Samsung USBC Headset (AKG) with VID/PID (0x04e8/0xa051) without the lsusb -v of the device in question. But from the description Chihhao Chen gave in the original message, I'm *guessing* the Clock Source for the Samsung USB Headset (AKG) runs at 48000hz and that we'd see a 2x Clock Multiplier in the lsusb -v This is all a wild guess, without the lsusb -v it's impossible to be sure, but if I'm right then the valid setting for the Microphone's Clock Selector is the Clock Multiplier, not the Clock Source, which, remember, runs at half the clock, hence why Chihhao Chen sees half the data rate for USB IN. Unfortunately our kernel code presently *does* always set the Clock Selector to the Clock Source, which is a bad assumption to make in my humble opinion. The only valid case for setting the Clock Selector to the Clock Source is when there's precisely one Clock Selector, precisely one Clock Source and no Clock Multipliers. In that special case we may be able to touch the setting of the only Clock Selector to match the only Clock Source. And, frankly, the only reason we're forced to do that explicitly is because some Behringer gear (Archwave AG DACs) gets confused and seems to somehow keep the old rate on the Clock Selector upon sample rate change. Thank you, Geraldo Nascimento
_______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel