From: Julien Grall <julien.grall@arm.com>
To: Andre Przywara <andre.przywara@arm.com>,
Stewart Hildebrand <stewart.hildebrand@dornerworks.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>,
Jan Beulich <jbeulich@suse.com>,
xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH v2 1/2] ns16550: Add compatible string for Raspberry Pi 4
Date: Wed, 31 Jul 2019 13:00:44 +0100 [thread overview]
Message-ID: <28ba4890-65c4-8940-8dc4-03cbff91c02c@arm.com> (raw)
In-Reply-To: <20190729170643.4ac19952@donnerap.cambridge.arm.com>
Hi,
On 29/07/2019 17:06, Andre Przywara wrote:
> On Mon, 29 Jul 2019 09:19:19 -0400
> Stewart Hildebrand <stewart.hildebrand@dornerworks.com> wrote:
>
> Hi,
>
>> Per the BCM2835 peripherals datasheet [1] page 10:
>> "The UART core is build to emulate 16550 behaviour ... The implemented
>> UART is not a 16650 compatible UART However as far as possible the
>> first 8 control and status registers are laid out like a 16550 UART. Al
>> 16550 register bits which are not supported can be written but will be
>> ignored and read back as 0. All control bits for simple UART receive/
>> transmit operations are available."
>>
>> Additionally, Linux uses the 8250/16550 driver for the aux UART [2].
>>
>> Unfortunately the brcm,bcm2835-aux-uart device tree binding doesn't
>> have the reg-shift and reg-io-width properties [3]. Thus, the reg-shift
>> and reg-io-width properties are inherent properties of this UART.
>>
>> Thanks to Andre Przywara for contributing the reg-shift and
>> reg-io-width setting snippet.
>>
>> In my testing, I have relied on enable_uart=1 being set in config.txt,
>> a configuration file read by the Raspberry Pi's firmware. With
>> enable_uart=1, the firmware performs UART initialization.
>>
>> [1] https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2835/BCM2835-ARM-Peripherals.pdf
>> [2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/tty/serial/8250/8250_bcm2835aux.c
>> [3] https://www.kernel.org/doc/Documentation/devicetree/bindings/serial/brcm,bcm2835-aux-uart.txt
>>
>> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@dornerworks.com>
>
> Reviewed-by: Andre Przywara <andre.przywara@arm.com>
> Tested-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Cheers,
--
Julien Grall
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next prev parent reply other threads:[~2019-07-31 12:01 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 13:19 [Xen-devel] [PATCH v2 0/2] Raspberry Pi 4 support Stewart Hildebrand
2019-07-29 13:19 ` [Xen-devel] [PATCH v2 1/2] ns16550: Add compatible string for Raspberry Pi 4 Stewart Hildebrand
2019-07-29 16:06 ` Andre Przywara
2019-07-31 12:00 ` Julien Grall [this message]
2019-07-29 13:19 ` [Xen-devel] [PATCH v2 2/2] xen/arm: platform: Add Raspberry Pi platform Stewart Hildebrand
2019-07-31 12:03 ` Julien Grall
2019-07-31 13:55 ` Stewart Hildebrand
2019-07-31 14:42 ` Julien Grall
2019-07-31 12:05 ` [Xen-devel] [PATCH v2 0/2] Raspberry Pi 4 support Julien Grall
2019-07-31 19:22 ` Julien Grall
2019-07-31 12:32 ` Andre Przywara
2019-07-31 15:03 ` Stewart Hildebrand
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