[rtc-linux] Re: [PATCH v2 1/2] rtc: ds1302: add register access abstraction layer

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

Forgot to add Mark in Cc:

On 27/06/2016 at 14:44:32 +0200, Alexandre Belloni wrote :
> On 27/06/2016 at 14:50:49 +0300, Sergei Ianovich wrote :
> > On Mon, 2016-06-27 at 20:19 +0900, Akinobu Mita wrote:
> > > The rtc-ds1302 driver now implemented using SPI 3wire mode.
> > > But I would like to access it with using three wires connected to
> > > GPIO
> > > lines.
> > >=20
> > > This adds abstraction layer for DS1302 register access in order to
> > > prepare to support for using GPIO lines.=C2=A0=C2=A0This enables to s=
hare
> > > common
> > > code between SPI driver and GPIO driver.
> >=20
> > I don't think this is the right way. DS-1302 is an SPI device, not a
> > GPIO one. It can be connected to a hardware SPI controller or a
> > software one (on top of GPIO or memory).
> >=20
> > Your patch re-adds Microwire SPI control logic to RTC subsystem, which
> > was cleared by my rewrite of drivers/rtc/rtc-ds1302.c. The logic is
> > already present in=C2=A0bitbang_txrx_be_cpha0_lsb() in=C2=A0drivers/spi=
/spi-
> > lp8841-rtc.c.
> >=20
> > I still think you need to implement=C2=A0spi-gpio-3wire with LSB-first
> > support in SPI subsystem instead. It wasn't done when I was adding
> > LP8841 support, because LP8841 was the only use case of Microwire SPI
> > control logic. If you add it, drivers/spi/spi-lp8841-rtc.c can be
> > removed and replaced by a GPIO driver to host a new spi-gpio-3wire
> > device.
>=20
> Well, back in April, we concluded it was not easily doable after
> discussing with Mark and there was still issues after implementing it in
> spi-gpio.
>=20
> My understanding is that while microwire seems compatible with SPI mode
> 0, it actually isn't and this should be treated as a different mode.
> If we want to do something generic, I think we should have a
> microwire-gpio driver. Maybe in the SPI subsystem?
>=20
> How do yo currently select microwire mode for PX270?
>=20
> --=20
> Alexandre Belloni, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com

--=20
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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