On Fri, Nov 15, 2019 at 11:21:53AM +0800, Greg Kroah-Hartman wrote:

On Thu, Nov 14, 2019 at 08:02:34AM -0600, Bin Liu wrote:

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On Thu, Nov 14, 2019 at 11:20:18AM +0800, Greg Kroah-Hartman wrote:

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On Tue, Nov 12, 2019 at 09:28:57AM -0600, Bin Liu wrote:

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Hi,

On Tue, Nov 12, 2019 at 02:51:51PM +0800, Chunfeng Yun wrote:

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Now the USB gadget subsystem can use the USB debugfs root directory,
so move musb's directory from the root of the debugfs filesystem into
the root of usb

My opinion is this move is unnecessary. I breaks existing debug tools or
documentation which is already published on Internet. 

Having a "root" directory for a single random driver seems like you are
making your driver a "very important" thing in the overall scheme of the
kernel, right?  What's wrong with using the usb subdirectory like all

Agree, it wasn't the right thing to do at the first place. But now
changing it adds support burden, because people very often refer to the
old information on the internet which no longer matches to the new
location. Basically, it is a cost of ABI change.

What information says that /sys/kernel/debug/mdev/ is the location for
this?  Is it in-kernel?

No, they are not in-kernel, but many places mainly on https://e2e.ti.com
and http://processors.wiki.ti.com. It basically says to get musb
regdump, cat /sys/kernel/debug/musb-hdrc.{0,1}/regdump, or to enter test
mode, do echo _testmode_ > /sys/kernel/debug/musb-hdrc.{0,1}/testmode...

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other USB drivers use (after this patch series is merged)?  That feels
like a much more "sane" way to handle the wide-open debugfs namespace.

Though I commented on this musb patch, my opinion is for this whole
series, either drop the whole series or apply the whole series.

I've applied all but this one and 2 others that did not build properly.

Okay.

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Yes, there are no rules when it comes to debugfs file names and
locations, but let's try to be sane please.

Fine with me. I can still support questions such as "can't open
/sys/kernel/debug/musb-hdrc.0/testmode: No such file or directory".

What tool looks for that?

I wrote a usb diagnosis tool called chkusb.sh, which basically checks
usb related information in
  - /proc/config.gz
  - /lib/modules/`uname -r`/kernel/drivers/
  - /proc/device-tree/
  - /sys/device/
  - /sys/kernel/debug/

So whenever I got a report on e2e.ti.com saying that usb doesn't work, I
just post this script and get a log which would give a clue if there was
any fundamental mistake in kernel configuration or deployment.

But not a big issue here for this tool regarding this patch set, I can
update the script to check both locations - /sys/kernel/debug/ and
/sys/kernel/debug/usb/.

-Bin.

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