Re: [PATCH] gpio: exar set value handling for hw with gpio pull-up or pull-down

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Tue, Aug 13, 2024 at 10:07:37AM -0500, Matthew McClain wrote:
> On 8/12/24 12:22, Andy Shevchenko wrote:
> > On Tue, Jul 30, 2024 at 07:16:10PM +0530, Sai Kumar Cholleti wrote:
> >
> > Please, refer to the functions in the text as func(), e.g.
> exar_set_value().
> > Use proper acronym, i.e. GPIO (capitalised).
> 
> We will update the patch and send a new version out if the current
> approach is acceptable.
> 
> >> Before the gpio direction is changed from input to output,
> >> exar_set_value is set to 1, but since direction is input when
> >> exar_set_value is called, _regmap_update_bits reads a 1 due to an
> >> external pull-up.  When force_write is not set (regmap_set_bits has
> >> force_write = false), the value is not written.  When the direction is
> >> then changed, the gpio becomes an output with the value of 0 (the
> >> hardware default).
> >>
> >> regmap_write_bits sets force_write = true, so the value is always
> >> written by exar_set_value and an external pull-up doesn't affect the
> >> outcome of setting direction = high.
> 
> > Okay, shouldn't you instead mark the respective registers as volatile or
> so?
> > I believe regmap has some settings for this case. But I haven't checked
> myself.
> 
> Unfortunately, in addition to marking the regmap volatile, we'd need to
> define reg_update_bits which means we'd be partially undoing the work
> from 36fb7218e87833b17e3042e77f3b102c75129e8f to reuse regmap locking
> and update functions.
> 
> Below is the relevant section of _regmap_update_bits().
> 
> static int _regmap_update_bits(struct regmap *map, unsigned int reg,
>                                unsigned int mask, unsigned int val,
>                                bool *change, bool force_write)
> ...
>         if (regmap_volatile(map, reg) && map->reg_update_bits) {
> ...
>         } else {
> ...
>                 if (force_write || (tmp != orig) || map->force_write_field)
> {
>                         ret = _regmap_write(map, reg, tmp);
>                         if (ret == 0 && change)
>                                 *change = true;
> ...
> 
> I suspect this might be a common problem with other GPIO drivers as
> well.

Sorry, this message went to cracks somehow. Can you update the commit
message and comments as mentioned above, add Fixes tag and send a v2
for a review. Also use 'gpio: exar: ...' in the Subject.

-- 
With Best Regards,
Andy Shevchenko