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Message-ID: <1ab280c2-2536-f507-8e12-2e4d3f3eb37e@yoseli.org>
Date:   Thu, 11 May 2023 18:07:34 +0200
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Subject: Re: pca953x issue when driving a DSI bridge
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org,
        brgl@bgdev.pl, linus.walleij@linaro.org
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From:   Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
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Hi Andy,

On 11/05/2023 09:49, Andy Shevchenko wrote:
> On Wed, May 10, 2023 at 11:18 PM Jean-Michel Hautbois
> <jeanmichel.hautbois@yoseli.org> wrote:
>> On 10/05/2023 19:25, andy.shevchenko@gmail.com wrote:
>>> Wed, May 10, 2023 at 06:12:19PM +0200, Jean-Michel Hautbois kirjoitti:
> 
> ...
> 
>>>> [   11.273968]  gpiod_set_value+0x5c/0xcc
>>>> [   11.277722]  ti_sn65dsi86_resume+0x4c/0x94 [ti_sn65dsi86]
>>>
>>> Your problem even worse, i.e. ->resume() might sleep.
>>
>> Indeed it is worse ;-).
>>
>>>> [   11.283131]  __rpm_callback+0x48/0x19c
>>>> [   11.286885]  rpm_callback+0x6c/0x80
>>>> [   11.290375]  rpm_resume+0x3b0/0x660
>>>> [   11.293864]  __pm_runtime_resume+0x4c/0x90
>>>> [   11.297960]  __device_attach+0x90/0x1e4
>>>> [   11.301797]  device_initial_probe+0x14/0x20
>>>> [   11.305980]  bus_probe_device+0x9c/0xa4
>>>> [   11.309817]  device_add+0x3d8/0x820
>>>> [   11.313308]  __auxiliary_device_add+0x40/0xa0
>>>> [   11.317668]  ti_sn65dsi86_add_aux_device.isra.0+0xb0/0xe0 [ti_sn65dsi86]
>>>> [   11.324381]  ti_sn65dsi86_probe+0x20c/0x2ec [ti_sn65dsi86]
>>>> [   11.329876]  i2c_device_probe+0x3b8/0x3f0
>>>> [   11.333889]  really_probe+0xc0/0x3dc
> 
> ...
> 
>>>> I suppose this is not a corner case and we may have other drivers and other
>>>> boards connecting a GPIO which can sleep in a context where it should not ?
>>>>
>>>> I would like to add one thing: on this board, the expander is routed in a
>>>> way that makes it impossible to "sleep" as the reset is forced pulled-up and
>>>> the power regulators are fixed and can't be stopped.
>>>
>>> Can you elaborate why you think there is a problem?
>>
>> I didn't know if it could be an issue or not, so I mentioned it but
>> sounds like a nonsense :-).
> 
> Maybe not. I don't know that hardware, schematics and more information
> is needed to understand. But I leave it to you.
> 
>>>> I don't know how to address this issue nicely and any thoughts is
>>>> appreciated !
>>>
>>> As a workaround you can consider the code around i2c_in_atomic_xfer_mode()
>>> but since I have heard about i.MX8 so many negative remarks which makes me
>>> think that hardware is a train wreck and shouldn't be used at all.
> 
>> Not sure to get the workaround proposal right...
> 
> There are possibilities to have atomic I2C transfers, but as comment
> says (on top of the above mentioned function) that is only for PMIC
> communications at the system shutdown.
> 
> In your case I would try the easiest way (taking into account that
> hardware connection is not preventing us from sleeping context), i.e.
> check if the function that has GPIO call may sleep on its own and
> simply replace gpiod_set_value() by gpiod_set_value_cansleep().
> 

And I found a patch, which is merged in v6.4-rc1 which does exactly this !
https://lore.kernel.org/all/20230405135127.769665-1-alexander.stein@ew.tq-group.com/

Thanks as it is your advice which made me find it :-p

JM