Re: pca953x issue when driving a DSI bridge

[Jean-Michel Hautbois]

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@xxxxxxxxxx> wrote:
> > On 10/05/2023 19:25, andy.shevchenko@xxxxxxxxx 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@xxxxxxxxxxxxxxx/

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

JM