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

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

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 sha=
re
> > 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/s=
pi-
> 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.

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.

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?

How do yo currently select microwire mode for PX270?

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

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