Re: [PATCH v7] usb: dwc3: core: Workaround for CSR read timeout

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Fri, Jun 21, 2024, Greg KH wrote:
> On Fri, Jun 21, 2024 at 05:42:42AM +0000, Thinh Nguyen wrote:
> > On Fri, Jun 21, 2024, Greg KH wrote:
> > > On Fri, Jun 21, 2024 at 09:40:10AM +0800, joswang wrote:
> > > > On Fri, Jun 21, 2024 at 1:16 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > > >
> > > > > On Wed, Jun 19, 2024 at 07:45:29PM +0800, joswang wrote:
> > > > > > From: Jos Wang <joswang@lenovo.com>
> > > > > >
> > > > > > This is a workaround for STAR 4846132, which only affects
> > > > > > DWC_usb31 version2.00a operating in host mode.
> > > > > >
> > > > > > There is a problem in DWC_usb31 version 2.00a operating
> > > > > > in host mode that would cause a CSR read timeout When CSR
> > > > > > read coincides with RAM Clock Gating Entry. By disable
> > > > > > Clock Gating, sacrificing power consumption for normal
> > > > > > operation.
> > > > > >
> > > > > > Cc: stable@vger.kernel.org
> > > > > > Signed-off-by: Jos Wang <joswang@lenovo.com>
> > > > >
> > > > > What commit id does this fix?  How far back should it be backported in
> > > > > the stable releases?
> > > > >
> > > > > thanks,
> > > > >
> > > > > greg k-h
> > > > 
> > > > Hello Greg Thinh
> > > > 
> > > > It seems first begin from the commit 1e43c86d84fb ("usb: dwc3: core:
> > > > Add DWC31 version 2.00a controller")
> > > > in 6.8.0-rc6 branch ?
> > > 
> > > That commit showed up in 6.9, not 6.8.  And if so, please resend with a
> > > proper "Fixes:" tag.
> > > 
> > 
> > This patch workarounds the controller's issue.
> 
> So it fixes a bug?  Or does not fix a bug?  I'm confused.

The bug is not a driver's bug. The fix applies to a hardware bug and not
any particular commit that can be referenced with a "Fixes" tag.

> 
> > It doesn't resolve any
> > particular commit that requires a "Fixes" tag. So, this should go on
> > "next". It can be backported as needed.
> 
> Who would do the backporting and when?

For anyone who doesn't use mainline kernel that needs this patch
backported to their kernel version.

> 
> > If it's to be backported, it can
> > probably go back to as far as v4.3, to commit 690fb3718a70 ("usb: dwc3:
> > Support Synopsys USB 3.1 IP"). But you'd need to collect all the
> > dependencies including the commit mention above.
> 
> I don't understand, sorry.  Is this just a normal "evolve the driver to
> work better" change, or is it a "fix broken code" change, or is it
> something else?
> 
> In other words, what do you want to see happen to this?  What tree(s)
> would you want it applied to?
> 

It's up to you, but it seems to fit "usb-testing" branch more since it
doesn't have a "Fixes" tag. The severity of this fix is debatable since
it doesn't apply to every DWC_usb31 configuration or every scenario.

Thanks,
Thinh