On 8 December 2014 at 16:41, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Monday 08 December 2014 16:23:01 Rafał Miłecki wrote: >> On 8 December 2014 at 16:03, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: >> > 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? >> >> 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 > > I think the suggestion was to use the spi-gpio driver in combination > with gpio-74x164. Oh, OK, I've obviously missed that. I don't know... I'm somehow not really convinced to that, because AFAIK there isn't any SPI master device between GPIOs and 'HC595. I don't know if pretending there is some extra hardware (just to use another Linux driver/layer) is a good idea. This would: 1) Not match hardware design 2) Involve some extra code. I'm not even sure if this would work out-of-the box (without some extra changes) at all. From early look at spi-gpio.c I can't see it implementing everything I need for GPIO-connected 'HC595. I think that implementing support for this extra SPI layer will actually require more code/tricks than a separated driver. -- Rafał -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
