[U-Boot] [PATCH 3/5] spi: add spi-mem driver for MediaTek MT7629 SoC

[Weijie Gao <weijie.gao@mediatek.com>]

On Mon, 2019-04-29 at 08:50 +0800, Weijie Gao wrote:
> On Sun, 2019-04-28 at 17:30 +0530, Jagan Teki wrote:
> > On Sun, Apr 28, 2019 at 6:54 AM Weijie Gao <weijie.gao@mediatek.com> wrote:
> > >
> > > On Sat, 2019-04-27 at 21:38 +0530, Jagan Teki wrote:
> > > > On Fri, Apr 26, 2019 at 2:53 PM Weijie Gao <weijie.gao@mediatek.com> wrote:
> > > > >
> > > > > This patch adds spi-mem driver for MediaTek MT7629 SoC to access SPI-NOR
> > > > > and SPI-NAND flashes.
> > > > >
> > > > > Cc: Jagan Teki <jagan@openedev.com>
> > > > > Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>
> > > > > ---
> > > > >  drivers/spi/Kconfig      |   9 ++
> > > > >  drivers/spi/Makefile     |   1 +
> > > > >  drivers/spi/mtk_spimem.c | 325 +++++++++++++++++++++++++++++++++++++++++++++++
> > > >
> > > > Do we really need spimen on the name? I prefer spi as it is, what is
> > > > the notation used by Linux I think spi itself, please check it.
> > >
> > > This controller is originally designed for accessing SPI-NAND flashes.
> > > How about the name mtk-snfi, which means Serial NAND(NOR) flash
> > > interface?
> > 
> > is the same name used in Linux?
> 
> This driver currently doesn't exist in Linux.

Linux kernel still uses the original mtk_qspi driver (mtk-quadspi),
because the spi-nor framework in kernel provides abstract interfaces
(not spi-mem) for high-level spi flash controllers.

Before u-boot switched to the spi-nor framework from kernel, the
mtk_qspi was able to work only with the old spi flash driver, with some
hacks.

We have to introduce new spi-mem driver to replace mtk_qspi for u-boot
because its spi-nor framework doesn't provide abstract interfaces and
uses only spi-mem interface. mtk_qspi can no longer work and can not be
modified for spi-mem framework.

For MT7629, the spi-nor controller (mtk_qspi) and spi-nand controller
(mtk-snfi) share the same spi pins controlled by a pinmux. This is the
reason we choose the snfi to control the spi-nor flash, by implementing
it as a spi-mem driver.

This new driver switches pinmux to snfi before transmission and back to
snor after transmission. So there's no side effects on other modules.