Re: [PATCH v1 1/2] fbtft: Rectify GPIO handling

[Andy Shevchenko]

On Fri, Apr 16, 2021 at 02:51:59PM +0200, Greg Kroah-Hartman wrote:
> On Fri, Apr 16, 2021 at 03:31:16PM +0300, Andy Shevchenko wrote:
> > The infamous commit c440eee1a7a1 ("Staging: fbtft: Switch to
> > the GPIO descriptor interface") broke GPIO handling completely.
> > It has already four commits to rectify and it seems not enough.
> > In order to fix the mess here we:
> > 
> >   1) Set default to "inactive" for all requested pins
> > 
> >   2) Fix CS, RD, and WR pins polarity since it's active low and
> >      GPIO descriptor interface takes it into consideration from
> >      the Device Tree or ACPI
> > 
> >   3) Fix RESET pin polarity in the places missed by the commit
> >      b918d1c27066 ("Staging: fbtft: Fix reset assertion when using gpio descriptor")
> > 
> >   4) Consolidate chip activation (CS assert) under default
> >      ->reset() callback
> > 
> > To summarize the expectations about polarity for GPIOs:
> > 
> >    #RD			Low
> >    #WR			Low
> >    #CS			Low
> >    #RESET		Low
> >    DC or RS		High
> >    RW			High
> >    Data	0..15		High
> > 
> > See also Adafruit learning course [1] for the example of the schematics.
> > 
> > While at it, drop unneeded NULL checks, since GPIO API is tolerant to that.
> > At the end, update TODO to mark this job eventually done.
> > 
> > [1]: https://learn.adafruit.com/adafruit-2-8-and-3-2-color-tft-touchscreen-breakout-v2/downloads
> 
> Shouldn't this be broken up into "one patch per thing" from your list
> above?  Feels like you did a lot of different things all in the same
> patch :(

I am aware, but breaking to the things here will bring it to the state where
the functionality is still broken in between. Another point is that the drop
of unneeded checks will bring the modification of the same line in the code
twice. Or if you look at 5), for instance, due to CS management breakage,
fixing it w/o 5) will bring it to the weird case that previously handled CS
due to lucky defaults from firmware or bootloader, suddenly won't work and
nothing can help it. The split in this case would look like adding the CS
handling to all drivers followed by removal all of them. I think it's ugly.
And so on. Believe me, I really tried hard to split this, but it always
becomes to undesired result.

Any ideas how to split that we fix stuff in one commit?


-- 
With Best Regards,
Andy Shevchenko