linux-kernel - Re: [PATCH] dmaengine: ti: omap-dma: Configure LCH

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Date:   Sat, 24 Nov 2018 19:29:28 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Aaro Koskinen <aaro.koskinen@....fi>
Cc:     Greg KH <greg@...ah.com>, Peter Ujfalusi <peter.ujfalusi@...com>,
        vkoul@...nel.org, dan.j.williams@...el.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        tony@...mide.com, linux-omap@...r.kernel.org,
        Felipe Balbi <felipe.balbi@...ux.intel.com>
Subject: Re: [PATCH] dmaengine: ti: omap-dma: Configure LCH_TYPE for OMAP1

On Sat, Nov 24, 2018 at 09:06:48PM +0200, Aaro Koskinen wrote:
> Hello,
> 
> On Sat, Nov 24, 2018 at 05:48:23PM +0000, Russell King - ARM Linux wrote:
> > Hmm, there's more questionable stuff in this driver, and the gadget
> > layer.
> 
> [...]
> 
> > So, whatever way I look at this, the code in the removal path both
> > in omap_udc and the gadget removal code higher up looks very wrong
> > and broken to me.
> 
> Yes, week ago I saw omap_udc crashing on both probe failure and
> module removal and sent some fixes for the most obvious failures (see
> https://marc.info/?l=linux-usb&m=154258778316932&w=2).

The effect of your patch is basically to replace the release function
with a no-op function.

> Is there any good driver that uses usb_add_gadget_udc_release() correctly?
> Looking at fsl_qe_udc.c and fsl_udc_core.c they should also crash if
> usb_add_gadget_udc_release() fails.

usb_add_gadget_udc_release() itself will call the release function
automatically on error.

The release function should _also_ be called when usb_del_gadget_udc()
is called (and would be guaranteed if the memset() is removed.)

So, moving the cleanup in the remove path into the release function
would solve the problem with omap_udc, and removing the memset()
would solve the problem with the core code.

It does leave a problem if the omap_udc module is removed - the
release function _could_ be called after the module has been removed
which would lead to an oops.  That's presumably why there's a
completion.  One solution to that would be to move the assignment
of udc->done before the call to usb_del_gadget_udc().

However, using a completion for something like this tends to be
frowned upon, but I don't see any other way to ensure correctness
here.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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