Re: [PATCH] usb: gadget: udc: renesas_usb3: Fix RZ/V2M {modprobe,bind} error

From: Marc Zyngier
Date: Mon May 29 2023 - 05:09:58 EST

On Mon, 29 May 2023 09:42:34 +0100,
Biju Das <biju.das.jz@xxxxxxxxxxxxxx> wrote:
> Hi Laurent,
> Thanks for the feedback.
> > Subject: Re: [PATCH] usb: gadget: udc: renesas_usb3: Fix RZ/V2M
> > {modprobe,bind} error
> >
> > Hi Biju,
> >
> > Thank you for the patch.
> >
> > On Fri, May 26, 2023 at 03:36:15PM +0100, Biju Das wrote:
> > > Currently {modprobe, bind} after {rmmod, unbind} results in probe
> > failure.
> > >
> > > genirq: Flags mismatch irq 22. 00000004 (85070400.usb3drd) vs.
> > > 00000004 (85070400.usb3drd)
> > > renesas_usb3: probe of 85070000.usb3peri failed with error -16
> > >
> > > Fix this issue by replacing "parent dev"->"dev" as the irq resource is
> > > managed by this driver.
> >
> > If the dev pointer passed to devm_request_irq() is not the correct one,
> > how does it work the first time the driver is loaded ?
> + Marc/ to give some feedback on this issue
> I believe there may be a bug in the genirq (kernel/irq) driver.
> first time it works ok. Maybe this driver is caching on unload
> with null value and comparing with actual one (irq 22) during reload??
> Maybe genirq expert can comment what went wrong here??

You get shouted at because you are registering an interrupt handler
for the same IRQ twice, and the interrupt is not configured with the
SHARED flag. If, as I understand it, you only have a single device
using this interrupt, then it means your driver is not freeing its
interrupt on unload.

And that's probably because the device object used when requesting the
interrupt isn't the one you load/unload, as indicated by the message.
On the first load of "usb3peri", you register an interrupt with
"usb3drd" as the requester device. You then unload "usb3peri", which
of course has no effect whatsoever on the interrupt.

You could simply have done a "cat /proc/interrupt" and see that
interrupt was still there after unload.

So the only bug here is in the handling of the interrupt request. And
that bug firmly lies in your code. My "expert" advise is to debug the
problem rather than suspecting some random failure modes.



Without deviation from the norm, progress is not possible.