Re: [PATCH v1 5/5] pinctrl: microchip-sgpio: wait until output is actually set

[Horatiu Vultur <horatiu.vultur@xxxxxxxxxxxxx>]

The 02/25/2022 12:29, Michael Walle wrote:
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Hi Michael,

Sorry for late reply.

> 
> Hi Horatiu,
> 
> Am 2022-02-25 10:24, schrieb Horatiu Vultur:
> > The 02/24/2022 17:10, Michael Walle wrote:
> > > Right now, when a gpio value is set, the actual hardware pin gets set
> > > asynchronously. When linux write the output register, it takes some
> > > time
> > > until it is actually propagated to the output shift registers. If that
> > > output port is connected to an I2C mux for example, the linux driver
> > > assumes the I2C bus is already switched although it is not.
> > > 
> > > Fortunately, there is a single shot mode with a feedback: you can
> > > trigger the single shot and the hardware will clear that bit once it
> > > has
> > > finished the clocking and strobed the load signal of the shift
> > > registers. This can take a considerable amount of time though.
> > > Measuremens have shown that it takes up to a whole burst cycle gap
> > > which
> > > is about 50ms on the largest setting. Therefore, we have to mark the
> > > output bank as sleepable. To avoid unnecessary waiting, just trigger
> > > the
> > > single shot if the value was actually changed.
> > 
> > I have tested this patch series on our lan9668 board and it worked
> > fine. Thanks!
> 
> Thanks for testing!
> 
> > I just have few questions:
> > 1. What about other boards/chips that have this sgpio, do they have
> > also
> >    the same issue? Because from what I recall on sparx5 they don't have
> >    this issue. I have seen it only on lan9668.
> 
> Unfortunatly, I don't have any knowledge what IP core is used in
> which SoC. I assumed the lan9668 used the same as the sparx5. If
> that is not the case, we need a new compatible. Do you know if it
> the same?