From: arnd@arndb.de (Arnd Bergmann)
To: linux-arm-kernel@lists.infradead.org
Subject: [RFC PATCH 1/1] drivers: introduce ARM SBSA generic UART driver
Date: Tue, 02 Sep 2014 15:48:06 +0200 [thread overview]
Message-ID: <3749748.k4a1nSHDdj@wuerfel> (raw)
In-Reply-To: <CAL_Jsq+Rs5MXC7s7EeWAEAPxxqaShAVGt=cdQxud5Us+-Zp6jw@mail.gmail.com>
On Tuesday 02 September 2014 08:20:53 Rob Herring wrote:
> >>
> >> This alone is not okay. There is no such implementation of hardware.
> >
> > But the SBSA explicitly allows this. I don't know of any vendor who just
> > implements the subset, but I've been told that this has been asked for.
>
> To use baudrate as an example, that must be configurable somehow
> either with pl011 registers or in a vendor specific way. I suppose you
> could do an actual implementation with all those things hardcoded in
> the design, but that seems unlikely.
Why does the baudrate need to be configurable? I think it's completely
reasonable to specify a console port that has a fixed (as in the
OS must not care) rate, and that can be implemented either as a UART
with a programmable rate or as a set of registers that directly talks
to a remote system management device over whatever hardware protocol
they choose.
> >> The DT must specify the implementation such as pl011.
> >
> > If it is a full featured PL011: sure. Then we don't need this driver at
> > all and just use the SBSA UART spec as a guideline for our earlycon
> > implementation.
> > I will try to learn if there is someone actually implementing only the
> > subset.
>
> I would have assumed you knew someone is. Otherwise, I don't really
> think anything should be implemented at this point. Perhaps adding
> SBSA uart as an explicit earlycon option would be worthwhile. Also, we
> should consider using ttySx instead of ttyAMAx for SBSA compliant
> systems (including ones with pl011).
What about systems that have both a SBSA debug port and a 8250
compatible UART? That sounds like a very realistic hardware design
choice for someone coming from an older x86/powerpc/mips/... chip
that has 8250 and adds the extra port for SBSA compliance.
Arnd
next prev parent reply other threads:[~2014-09-02 13:48 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-29 16:13 [RFC PATCH 0/1] ARM SBSA UART driver Andre Przywara
2014-08-29 16:13 ` [RFC PATCH 1/1] drivers: introduce ARM SBSA generic " Andre Przywara
2014-08-29 18:59 ` Arnd Bergmann
2014-08-29 23:10 ` Andre Przywara
2014-09-02 19:51 ` Arnd Bergmann
2014-09-05 14:11 ` Andre Przywara
2014-09-02 3:06 ` Rob Herring
2014-09-02 10:06 ` Andre Przywara
2014-09-02 10:46 ` Mark Rutland
2014-09-02 13:20 ` Rob Herring
2014-09-02 13:48 ` Arnd Bergmann [this message]
2014-09-02 17:38 ` Rob Herring
2014-09-02 19:34 ` Arnd Bergmann
2014-09-05 14:27 ` Andre Przywara
2014-09-05 14:37 ` Andre Przywara
2014-09-02 18:19 ` Peter Hurley
2014-09-05 14:44 ` Andre Przywara
2014-09-05 15:24 ` Peter Hurley
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