Re: WG: [PATCH] usb: musb: omap2430: fix occasional musb breakage on boot

[Andreas Naumann <dev@andin.de>]

On 13.12.2013 13:34, Grazvydas Ignotas wrote:
> On Thu, Dec 12, 2013 at 11:29 PM, Andreas Naumann <dev@andin.de> wrote:
>> Hi Grazvydas,
>>
>>> Von: Grazvydas Ignotas [mailto:notasas@gmail.com]
>>> Gesendet: Donnerstag, 12. Dezember 2013 01:21
>>> An: linux-usb@vger.kernel.org
>>> Cc: Felipe Balbi; linux-omap@vger.kernel.org; Naumann Andreas; Grazvydas
>>> Ignotas; stable@vger.kernel.org
>>> Betreff: [PATCH] usb: musb: omap2430: fix occasional musb breakage on boot
>>>
>>>
>>> This is a hard to reproduce problem which leads to non-functional
>>> USB-OTG port in 0.1%-1% of all boots. Tracked it down to commit
>>> e25bec160158abe86c "omap2+: save and restore OTG_INTERFSEL",
>>> which introduces save/restore of OTG_INTERFSEL over suspend.
>>>
>>> Since the resume function is also called early in driver init, it uses a
>>> non-initialized value (which is 0 and a non-supported setting in DM37xx
>>> for INTERFSEL). Shortly after the correct value is set. Apparently this
>>> works most time, but not always.
>>>
>>> Fix it by not writing the value on runtime resume if it is 0
>>> (0 should never be saved in the context as it's invalid value,
>>> so we use it as an indicator that context hasn't been saved yet).
>>>
>>> This issue was originally found by Andreas Naumann:
>>> http://marc.info/?l=linux-usb&m=138562574719654&w=2
>>>
>>> Reported-and-bisected-by: Andreas Naumann <anaumann@ultratronik.de>
>>> Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
>>> Cc: <stable@vger.kernel.org>
>>> ---
>>> This is a regression from 3.2, so should go to -rc and stable, IMO.
>>> It's really annoying issue if you want to have a stable OTG behavior,
>>> I've burned quite a lot of time on it myself over a year ago and gave up
>>> eventually. Good thing Andreas finally found it, many thanks to him!
>>>
>>>    drivers/usb/musb/omap2430.c |    3 ++-
>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/usb/musb/omap2430.c b/drivers/usb/musb/omap2430.c
>>> index 2a408cd..737b3da 100644
>>> --- a/drivers/usb/musb/omap2430.c
>>> +++ b/drivers/usb/musb/omap2430.c
>>> @@ -672,7 +672,8 @@ static int omap2430_runtime_resume(struct device *dev)
>>>
>>>          if (musb) {
>>>                  omap2430_low_level_init(musb);
>>> -               musb_writel(musb->mregs, OTG_INTERFSEL,
>>> +               if (musb->context.otg_interfsel != 0)
>>> +                       musb_writel(musb->mregs, OTG_INTERFSEL,
>>>                                  musb->context.otg_interfsel);
>>>                  phy_power_on(musb->phy);
>>>          }
>>>
>>
>> Oh, easy way out. I like it but I've also been thinking about your comment
>> on my original post, which was that initializing otg_interfsel to the PHYSEL
>> bits only might be dangerous because we cant be sure that there are other
>> bits in the register.
>> However, isnt assuming that 0 is invalid on all OMAPs just as dangerous?
>
> Well I was trying to do a minimal fix so that it could be suitable for
> merging to stable kernels. But yes you're right, I've just checked
> OMAP4 TRM and 0 is actually valid value there..
>
>> After thinking about my patch again, I would propose to change otg_interfsel
>> into otg_physel and read-modify-write only those bits in resume() as you
>> suggested in your first answer. That way I could discard the problematic
>> first read in probe() while leaving other bits untouched. If you agree I
>> post a patch for this tomorrow.
>
> Hmm I don't know about that, this would be inconsistent with what all
> other OMAP drivers do. Maybe we should do what musb_core.c does just

Ok, thats cool.

> to be consistent and add a similar comment. Only the static variable
> could be avoided in favor of struct omap2430_glue member.

Whats wrong with the static?

cheers,
Andreas

>
> Gražvydas
>

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