linux-kernel - Re: [PATCH v6 0/5] usb: xhci: Add support for Renesas USB controllers

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Date:   Thu, 12 Mar 2020 12:26:36 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     Christian Lamparter <chunkeey@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        John Stultz <john.stultz@...aro.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        USB list <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Subject: Re: [PATCH v6 0/5] usb: xhci: Add support for Renesas USB controllers

On 04-02-20, 18:33, Mathias Nyman wrote:

> > > 
> > > There are a few other opens regarding this series. Mostly because I'm not (yet)
> > > familiar with all the details, so I'll just just list them here.
> > > 
> > > - Is it really enough to add the Renesas driver to Makefile before xhci-pci
> > >    driver to make sure it gets matched and probed based on vendor/device id
> > >    before xhci-pci driver is matched and probed based on pci class?
> > >    What if the Renesas driver is a module and xhci-pci compiled in?
> > 
> > The driver loading rules are based on level and makefile order. So
> > renesas will always be loaded before xhci driver. This is required since
> > xhci claims all devices, so we need to make sure it loads before.
> > 
> > I think we should make it inbuilt driver rather than a module. xhci
> > driver is only inbuilt.
> > 
> > If there is a better way to handle this, am all for it.
> > 
> > > - Previously probe didn't return before hcd's were added and everything set up.
> > >    Now with request_firmware_nowait() probe returns early successfully, and the
> > >    old xhci_pci_probe() which sets up everything is called later by the request
> > >    firmware callback. So there could be whole new set of races possible.
> > >    For example pci remove can be called mid firmware loading, or when the old
> > >    xhci_pci_probe is still setting up things.
> > 
> > I think this is a valid concern. Let me think about how to solve this..
> > maybe add a flag in remove which ensure remove doesnt run untill the
> > probe/firmware callback is completed.
> 
> How about initiating async firmware loading before probe is called by using
> DECLARE_PCI_FIXUP_*() hooks?

Well somehow that does not work :(

I tried using DECLARE_PCI_FIXUP_FINAL hook to request the firmware.
Doing so from probe works but from fixup fails always!

So expect this one, I have done the rest of the changes requested, will
send them over soon

Thanks
-- 
~Vinod