On Tue, Jul 30, 2019 at 04:25:56PM +0100, Thomas Preston wrote:

On 30/07/2019 15:19, Mark Brown wrote:

quoted

It is unclear what this mutex usefully protects, it only gets taken when
writing to the debugfs file to trigger this diagnostic mode but doesn't
do anything to control interactions with any other code path in the
driver.

If another process reads the debugfs node "diagnostic" while the turn-on 
diagnostic mode is running, this mutex prevents the second process
restarting the diagnostics.

This is redundant if debugfs reads are atomic, but I don't think they are.

Like I say it's not just debugfs though, there's the standard driver
interface too.