Re: pca953x issue when driving a DSI bridge

[Jean-Michel Hautbois]

Hi Andy,

On 10/05/2023 19:25, andy.shevchenko@xxxxxxxxx wrote:
> Wed, May 10, 2023 at 06:12:19PM +0200, Jean-Michel Hautbois kirjoitti:
> > Hello there !
> >
> > I have a custom board, based on a i.MX8mm SoC which has a MIPI-DSI to eDP
> > bridge (namely, a TI sn65dsi86). This bridge has a DSI enable pin, which is
> > basically its reset pin, connected to my PCA9539 GPIO expander.
> >
> > The issue is that this pin can't be sleeping, and it is tested in the
> > gpiod_set_value() function.
> >
> > Here is where it fails in my dmesg:
>
> ...
>
> > [   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 :-).

> > 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...
I won't argue about i.MX8 ;-).

Thanks,
JM