On 8 December 2014 at 16:03, Geert Uytterhoeven [off-list ref] wrote:

Hi Rafał,

On Mon, Dec 8, 2014 at 3:47 PM, Rafał Miłecki [off-list ref] wrote:

quoted

On 8 December 2014 at 15:41, Geert Uytterhoeven [off-list ref] wrote:

quoted

On Mon, Dec 8, 2014 at 3:27 PM, Rafał Miłecki [off-list ref] wrote:

quoted

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@gmail.com>
---
 .../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.

quoted

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?

It's not the missing OE support in gpio-74x164 that worries me, but
the whole rest.

I would need to modify gpio-74x164 to:
1) Use another OF table with different entry
2) Use different probe function that doesn't take spi_device parameter
and doesn't do spi setup
3) Extend struct gen_74x164_chip to include GPIOs
4) Use totally different __gen_74x164_write_config

Amount of shared code would be so small I doubt it's worth it. Both
driver are quite trivial (200 or less LOC). Sharing:
1) ~5 lines long __gen_74x164_write_config
2) ~5 lines long gen_74x164_set_value
3) 1 line long gen_74x164_direction_output
makes me feel it's not really worth combining these two drivers into a one.
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