Re: [PATCH] gpio: pca953x: Don't flip bits on PCA957x GPIO expanderswhen probing them.

[Graeme Smecher]

Hi Grant,

On 04/08/13 05:35 AM, Haojian Zhuang wrote:
> On Sat, Aug 3, 2013 at 5:24 AM, Graeme Smecher
> <gsmecher@xxxxxxxxxxxxxxxxxxx>  wrote:
> > The pca957x driver supports a handful of I2C GPIO expanders from NXP, Maxim,
> > and TI. For the PCA9574 and PCA9575 devices only, the driver resets the GPIO
> > level and direction in the pca957x_probe function. This seems like the wrong
> > thing to do, since it can cause hardware bit twiddles during warm reboots when
> > the chip state and reset values don't match.
> >
> > This kind of initialization is best left upstream (in a bootloader) or
> > downstream (in userspace). It's also an inconsistency across devices supported
> > by this driver.
> >
> > Signed-off-by: Graeme Smecher<gsmecher@xxxxxxxxxxxxxxxxxxx>
> > Cc: Grant Likely<grant.likely@xxxxxxxxxx>
> > Cc: Haojian Zhuang<haojian.zhuang@xxxxxxxxxxx>
> > ---
> >   drivers/gpio/gpio-pca953x.c |   11 -----------
> >   1 file changed, 11 deletions(-)
> >
> > diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
> > index 426c51d..47c08d8 100644
> > --- a/drivers/gpio/gpio-pca953x.c
> > +++ b/drivers/gpio/gpio-pca953x.c
> > @@ -683,17 +683,6 @@ static int device_pca957x_init(struct pca953x_chip *chip, u32 invert)
> >          int ret;
> >          u8 val[MAX_BANK];
> >
> > -       /* Let every port in proper state, that could save power */
> > -       memset(val, 0, NBANK(chip));
> > -       pca953x_write_regs(chip, PCA957X_PUPD, val);
> > -       memset(val, 0xFF, NBANK(chip));
> > -       pca953x_write_regs(chip, PCA957X_CFG, val);
> > -       memset(val, 0, NBANK(chip));
> > -       pca953x_write_regs(chip, PCA957X_OUT, val);
> > -
> > -       ret = pca953x_read_regs(chip, PCA957X_IN, val);
> > -       if (ret)
> > -               goto out;
> >          ret = pca953x_read_regs(chip, PCA957X_OUT, chip->reg_output);
> >          if (ret)
> >                  goto out;
> > --
> > 1.7.10.4
> Acked-by: Haojian Zhuang<haojian.zhuang@xxxxxxxxx>

Just a quick ping: I think you're the responsible maintainer for this 
patch, and I haven't seen it show up on git.secretlab.ca. Do you want me 
to resubmit with Haojian's e-mail corrected?

I should also note that this patch is NOT boot-tested. My hardware 
containing this part is only supported by the vendor's aging 2.6.37 
branch. (It's a custom ARM board using the TI AM3874.) The pca953x 
driver has evolved enough that the patches for 2.6.37 and mainline 
aren't identical, but they still rhyme.

thanks,
Graeme
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