linux-kernel - Re: [PATCH v2] gpio: add TS-5500 DIO blocks support

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Date:	Wed, 19 Dec 2012 17:13:47 -0500 (EST)
From:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	linux-kernel@...r.kernel.org,
	Jerome Oufella <jerome.oufella@...oirfairelinux.com>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v2] gpio: add TS-5500 DIO blocks support

Hi Grant,

> Please take a look at either send me a follow-on patch to convert it
> to use gpio-generic, or tell my why gpio-generic isn't appropriate here.

The gpio-generic driver is not appropriate here because Technologic Systems
x86-based platforms do not use a typical GPIO implementation. 
To name a few specificities:
- The GPIOs are available through ioport and not iomem
- There are input-only/output-only/input-output lines on the same block
- The number of GPIOs differs between blocks (currently 11, 13 and 14 pins)
- A single bit in a control register drives the direction of 4 input/output
  lines, while the register's other bits have different functions.

IMHO these considerations justify a specific GPIO driver to support these
Technologic Systems pin blocks.

Regards,
Vivien
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