[U-Boot] [PATCH V3] imx: mx25: Remove SION bit in all pin-mux that are safe

[Michael Trimarchi <michael@amarulasolutions.com>]

Hi Benoit

On Thu, Jan 25, 2018 at 10:48:42PM +0100, Benoît Thébaudeau wrote:
> Hi Michael,
> 
> On Thu, Jan 25, 2018 at 2:06 PM, Michael Trimarchi
> <michael@amarulasolutions.com> wrote:
> > SION bit should be used in the situation that we need
> > to read back the value of a pin and should not be set by
> > default macro.
> >
> > We get some malfunction as raised by following thread
> >
> > https://www.spinics.net/lists/linux-usb/msg162574.html
> >
> > As reported by this application note:
> > https://www.nxp.com/docs/en/application-note/AN5078.pdf
> >
> > The software input on (SION) bit is an option to force an input
> > path to be active regardless of the value driven by the
> > corresponding module. It is used when the nature direction
> > of a pin depending on selected alternative function is an output,
> > but it is needed to read the real logic value on a pin.
> >
> > The SION bit can be used in:
> > • Loopback: the module of a selected alternative function drives
> > the pad and also receives the pad value as an input
> > • GPIO capture: the module of a selected alternative function
> > drives the pin and the value is captured by the GPIO
> >
> > SION bit is not necessary when the pin is configured as a peripheral
> > apart specific silicon bug. If an application needs to have this
> > set, this should be done in board file or in dts file
> >
> > Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
> 
> [...]
> 
> I have now tested the following peripherals on i.MX25 without any SION
> bit set: AUDMUX/SSI, eSDHC, FEC (except PHY access for which MDIO
> might have an issue without SION; Ethernet works but I have not
> checked whether this is possible at least partially without access to
> the PHY registers), GPIO, I2C, SLCDC, UART, and USB. Everything worked
> fine except the lack of SION for eSDHC CMD, which is true for all
> eSDHC instances (and not only for eSDHC1, so Linux's
> arch/arm/boot/dts/imx25-pinfunc.h should be fixed). Therefore, SION is
> mandatory for all the eSDHC CMD functions in

I have checked and u-boot does not have this pin-muxing. I think that this
patch should go as it is and a separate patch like this one following should
be applied after that. What do you think?

> arch/arm/include/asm/arch-mx25/iomux-mx25.h, but it can be removed for
> everything else (I still have to carry out one more test to confirm
> this for FEC MDIO), and moved to the board files if necessary (but I
> don't think that any mainline board code is doing something fancy
> enough to need it).
> 
> If the bus-status detection example in the documentation of SION in
> the reference manual is useful, it means that SION is probably
> required for all the signals requiring simultaneous output and input
> (such as I²C for device clock stretching or multi-master bus
> arbitration, except if the IP toggles between input and output low at
> each clock edge rather than between open-drain output high and output
> low), because there are no automatic SION signals between the
> peripherals and the pads but only direction signals that can request a
> single direction at a time. For bidirectional signals that do not
> require simultaneous output and input because they work in turns (such
> as FEC MDIO), SION can be required or not depending on whether the IP
> toggles the direction signal for each turn or always expects an input
> feedback while driving an open-drain output high. Even if SION is
> required for the I²C example mentioned above (which is unlikely as
> basic I²C transfers work fine and clock stretching detection is
> automatic and would always need the input state), the need for these
> advanced I²C features can be considered board-specific, so SION would
> still not be required in iomux-mx25.h.
> 
> In the end, for this patch, apart from the pending test for FEC MDIO:
> Reviewed-by: Benoît Thébaudeau <benoit.thebaudeau.dev@gmail.com>
> 
> Best regards,
> Benoît