linux-kernel - Re: [PATCH v4 6/7] gpio: exar: switch to using regmap

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Date:   Tue, 10 Nov 2020 19:08:20 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        David Laight <David.Laight@...lab.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 6/7] gpio: exar: switch to using regmap

On Tue, Nov 10, 2020 at 05:52:26PM +0100, Bartosz Golaszewski wrote:
> On Tue, Nov 10, 2020 at 5:43 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> >
> > On Tue, Nov 10, 2020 at 6:37 PM Bartosz Golaszewski
> > <bgolaszewski@...libre.com> wrote:
> > > On Tue, Nov 10, 2020 at 5:17 PM Andy Shevchenko
> > > <andriy.shevchenko@...ux.intel.com> wrote:

...

> > It's not a typo. But thinking again. This is basically done in regmap
> > to support serial buses. Here we have MMIO pretty much with 32-bit or
> > 64-bit address accesses. I didn't dig into regmap implementation to
> > understand the consequences of changing this to the different values
> > (it seems like rather offset, and in this case 11 is a correct one,
> > not a typo, and regmap is okay with that).
> > But I would rather ask Jan to actually mount debugfs and dump
> > registers and see if it screws up the UART (because it may go all over
> > important registers), that's why I think this configuration is still
> > missing some strict rules about what addresses (offsets) driver may or
> > may not access.
> 
> Ok now I get it. Yes 11 seems to be right in this case for the max
> address. We can implement the readable/writable callbacks to be very
> strict about the register accesses but isn't it overkill? This driver
> is very small and only accesses a couple registers. I don't see such
> strict checking very often except for very complicated modules (like
> pca953x you mentioned).

Maybe a comment in commit message or code that this has no protection against
access to out of boundary registers.

Keep my tag after choosing 11 and whatever you decide for access to non-GPIO
registers from this driver. I'm not blocking this from upstreaming since we
have got a confirmation that main functionality works as expected.


-- 
With Best Regards,
Andy Shevchenko