From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Lee Jones <lee.jones@linaro.org>,
radu_nicolae.pirea@upb.ro, Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Nicolas Ferre <nicolas.ferre@microchip.com>,
Greg KH <gregkh@linuxfoundation.org>,
Mark Brown <broonie@kernel.org>, Jiri Slaby <jslaby@suse.com>,
Richard Genoud <richard.genoud@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
linux-spi <linux-spi@vger.kernel.org>
Subject: Re: [PATCH v12 0/6] Driver for at91 usart in spi mode
Date: Tue, 11 Sep 2018 21:04:56 +0200 [thread overview]
Message-ID: <CAMuHMdV_btX=HcTpfnrP6iUfrBNvQfDybE_tKtJZZERMQ8n=ZA@mail.gmail.com> (raw)
In-Reply-To: <20180911185839.GA25212@piout.net>
Hi Alexandre,
On Tue, Sep 11, 2018 at 8:58 PM Alexandre Belloni
<alexandre.belloni@bootlin.com> wrote:
> On 11/09/2018 19:39:30+0100, Lee Jones wrote:
> > On Tue, 11 Sep 2018, Geert Uytterhoeven wrote:
> >
> > > On Tue, Sep 11, 2018 at 5:36 PM Alexandre Belloni
> > > <alexandre.belloni@bootlin.com> wrote:
> > > > On 11/09/2018 16:59:09+0200, Geert Uytterhoeven wrote:
> > > > > On Tue, Sep 11, 2018 at 11:40 AM Alexandre Belloni
> > > > > <alexandre.belloni@bootlin.com> wrote:
> > > > > > Then you'd have multiple compatible strings for the same IP which is a
> > > > > > big no-no.
> > > > >
> > > > > It's still the same hardware device, isn't?
> > > > > What if the SPI or UART slave is not on-board, but on an expansion board?
> > > > > Then the SoC-specific .dtsi has no idea what mode should be used.
> > > > >
> > > > > Hence shouldn't the software derive the hardware mode from the full
> > > > > hardware description in DT? If that's impossible (I didn't look into detail
> > > > > whether an SPI bus can easily be distinguished from a UART bus), perhaps
> > > > > a mode property should be added?
> > > >
> > > > Yes, this is exactly what is done:
> > > >
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd.git/tree/drivers/mfd/at91-usart.c?h=ib-mfd-spi-tty-4.20-1#n33
> > >
> > > OK.
> > >
> > > I guess the main "hackish" part is that the mfd_cell uses of_compatible,
> > > which thus requires having additional compatible values?
> > >
> > > I think those can just be removed. AFAICS, the SPI and serial drivers already
> > > match against the "at91_usart_spi" resp. "atmel_usart_serial" platform device
> > > names?
> >
> > The hackish part of this driver is that it's using MFD for something
> > which is clearly not an MFD. It's a USART device. Nothing more,
> > nothing less.
> >
> > Does anyone have the datasheet to hand?
>
> It is not a simple usart, it is either a usart or a full blown SPI
> controller with registers changing layout depending on the selected
> mode. Otherwise, I'm not sure how you would get a USART to do SPI.
Note the "S" in USART. SPI is just synchronous serial with a shared clock
for transmit and receive. So the hardware is not that unrelated.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2018-09-11 19:05 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-04 11:13 [PATCH v12 0/6] Driver for at91 usart in spi mode Radu Pirea
2018-09-04 11:13 ` [PATCH v12 1/6] MAINTAINERS: add at91 usart mfd driver Radu Pirea
2018-09-04 11:13 ` [PATCH v12 2/6] dt-bindings: add binding for atmel-usart in SPI mode Radu Pirea
2018-09-04 11:13 ` [PATCH v12 3/6] mfd: at91-usart: added mfd driver for usart Radu Pirea
2018-09-04 11:13 ` [PATCH v12 4/6] MAINTAINERS: add at91 usart spi driver Radu Pirea
2018-09-04 11:13 ` [PATCH v12 5/6] spi: at91-usart: add driver for at91-usart as spi Radu Pirea
2018-09-04 11:13 ` [PATCH v12 6/6] tty/serial: atmel: change the driver to work under at91-usart mfd Radu Pirea
2018-09-10 9:48 ` [PATCH v12 0/6] Driver for at91 usart in spi mode Lee Jones
2018-09-10 9:51 ` Nicolas Ferre
2018-09-10 13:43 ` Lee Jones
2018-09-11 9:33 ` Lee Jones
2018-09-11 9:39 ` Alexandre Belloni
2018-09-11 14:59 ` Geert Uytterhoeven
2018-09-11 15:36 ` Alexandre Belloni
2018-09-11 16:23 ` Geert Uytterhoeven
2018-09-11 18:39 ` Lee Jones
2018-09-11 18:58 ` Alexandre Belloni
2018-09-11 19:04 ` Geert Uytterhoeven [this message]
2018-09-11 22:44 ` Lee Jones
2018-09-11 22:54 ` Lee Jones
2018-09-12 7:33 ` Alexandre Belloni
2018-09-12 8:41 ` Lee Jones
2018-09-12 9:43 ` Geert Uytterhoeven
2018-09-12 10:54 ` Lee Jones
2018-09-12 11:17 ` Alexandre Belloni
2018-09-12 11:43 ` Lee Jones
2018-09-12 12:14 ` Alexandre Belloni
2018-09-12 13:12 ` Lee Jones
2018-09-12 19:36 ` Radu Pirea
2018-10-09 9:04 ` Lee Jones
2018-09-11 18:59 ` Geert Uytterhoeven
2018-09-11 22:43 ` Lee Jones
2018-09-12 7:30 ` Alexandre Belloni
2018-09-12 8:36 ` Lee Jones
2018-09-11 11:18 ` [GIT PULL v2] Immutable branch between MFD, SPI and TTY due for the v4.20 merge window Lee Jones
2018-09-11 14:04 ` Greg KH
2018-09-11 14:07 ` Lee Jones
2018-09-11 14:12 ` Greg KH
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