[PATCH] pinctrl: fsl: imx: Check for 0 config register

[u.kleine-koenig@pengutronix.de (Uwe Kleine-König)]

On Mon, Mar 30, 2015 at 11:40:47AM +0200, Linus Walleij wrote:
> On Fri, Mar 27, 2015 at 11:32 AM, Stefan Agner <stefan@agner.ch> wrote:
> > On 2015-03-24 16:26, Markus Pargmann wrote:
> 
> >> 0 is used in all pinfunction definitions when a config register is not
> >> available, for example imx25-pinfunc.h. If a configuration value is used
> >> for such a pinfunction the driver will always write it to the
> >> configuration register if it is not -1. For a 0 configuration register
> >> the configuration value is written to offset 0x0. This can lead to a
> >> crashing/hanging system without any warning message.
> >
> > 0 is a valid offset for Vybrid's mux register, however, since Vybrid set
> > the SHARE_MUX_CONF_REG, intepreting a 0 in conf_reg as "not set"
> > actually works.
> >
> > What is a bit a bummer is that we now have different meanings of 0,
> > depending on the field:
> > - For the first field (mux), 0 is a valid offset
> > - For the second field (config), 0 means not valid
> 
> What is generally scary about DTS files is that the DT formats
> are not ruled by a context-free grammar.
> 
> There were attempts to formalize some bindings using BNF
> but they seems to have been given up.
> 
> We need to combat this by trying to be strict and logic ...
> I can't really understand from the discussion here whether
> the patch should be applied or not, so I'm not applying it
> until Stefan | Uwe gives an explicit ACK.
Acked-by: Uwe Kleine-K?nig <u.kleine-koenig@pengutronix.de>

I just have a small bad feeling because -1 and 0 both mean "no config
register". But that is a problem already there without Markus' patch.
And I see that this patch really fixes a problem. As Stefan sait it
should be fine for Vybrid I think applying it is the right thing to do
here.

Best regards
Uwe

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