Re: [PATCH] gpio: sn54hc595: new driver for GPIO shift registers chipsets

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Rafał,

On Mon, Dec 8, 2014 at 3:47 PM, Rafał Miłecki <zajec5@xxxxxxxxx> wrote:
> On 8 December 2014 at 15:41, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>> On Mon, Dec 8, 2014 at 3:27 PM, Rafał Miłecki <zajec5@xxxxxxxxx> wrote:
>>> SN54HC595 and SN74HC595 are devices based on shift registers controlled
>>> with 5 input signals (serial-in) and providing 8 outputs (parallel-out).
>>>
>>> They are present on some Broadcom home router boards where manufacturer
>>> needed few extra GPIOs.
>>>
>>> This driver simply uses specified GPIOs to control shift registers and
>>> registers another GPIO chip. So you can call it a GPIO extender.
>>>
>>> Due to the hardware design only output direction is supported. Reading
>>> values is handled using tiny internal cache.
>>>
>>> Signed-off-by: Rafał Miłecki <zajec5@xxxxxxxxx>
>>> ---
>>>  .../devicetree/bindings/gpio/gpio-sn54hc595.txt    |  35 ++++
>>>  drivers/gpio/Kconfig                               |  11 ++
>>>  drivers/gpio/Makefile                              |   1 +
>>>  drivers/gpio/gpio-sn54hc595.c                      | 219 +++++++++++++++++++++
>>
>> The '595 is already handled by drivers/gpio/gpio-74x164.c.
>
> gpio-74x164.c seems to be tight closely to the SPI. In my case it's
> GPIO-controller '595.

Right. gpio-74x164.c uses the SPI framework, so it will work with any SPI
master controller, while your driver contains a very simple variant (without any
timing constraints) of spi-gpio.c, and is limited to connecting to GPIO pins.

> Do you have any other idea how we could handle this?

Your driver does provide OE support, which gpio-74x164 doesn't support.
Perhaps that can be added to gpio-74x164 instead?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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                                -- Linus Torvalds
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