From: Julien Grall <julien.grall@arm.com>
To: Andre Przywara <andre.przywara@arm.com>,
Shanker Donthineni <shankerd@codeaurora.org>,
xen-devel <xen-devel@lists.xensource.com>,
=Stefano Stabellini <sstabellini@kernel.org>
Cc: Philip Elcan <pelcan@codeaurora.org>, Wei Chen <Wei.Chen@arm.com>,
Vikram Sethi <vikrams@codeaurora.org>,
Steve Capper <Steve.Capper@arm.com>
Subject: Re: [PATCH v2] arm/acpi: Add Server Base System Architecture UART support
Date: Wed, 1 Jun 2016 17:18:47 +0100 [thread overview]
Message-ID: <574F0AE7.3060701@arm.com> (raw)
In-Reply-To: <25202ba7-6b7c-989f-ee67-4be8c8068c77@arm.com>
Hi Andre,
On 01/06/16 16:56, Andre Przywara wrote:
>>> I would like to support both the interfaces
>>> (ACPI_DBG2_SBSA_32/ACPI_DBG2_SBSA) If you are okay.
>>
>> I am a bit puzzled, so your UART is only supporting 32-bit access (i.e
>> no 16-bit and 8-bit access)?
>
> Just to clarify: the SBSA spec is not very clear in this respect, as it
> only speaks of "a set of 32-bit registers". But this has been
> interpreted as "supports 32-bit accesses". So there was a patch lately
> in Linux to change all accesses to SBSA UARTs to 32-bit accessors
> (writel/readl), because there is at least this one mentioned platform
> that requires this, while all the other relevant platforms we could get
> hold of can also cope with 32-bit accesses. This may not be true for all
> legacy PL011 implementations out there, but for the SBSA subset this is
> deemed a safe assumption.
Thank you for the explanation.
> So if possible we should switch to 32-bit accessors for the SBSA UART.
The driver use 32-bit accessors exclusively.
>
>> If so your platform is based on SBSA v2.3, and therefore the PL011
>> driver needs more modification to support properly your platform. For
>> instance, the register UARTMIS is not present in v2.3 but used by the
>> driver.
>
> I think this has been changed in the spec lately, it was present in
> earlier revisions of the spec.
If so, I would replace the read to UARTMIS by a combination UARTIMSC and
UARTRIS to avoid any issue with the UART based on SBSA v2.3.
Cheers,
--
Julien Grall
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next prev parent reply other threads:[~2016-06-01 16:18 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-31 14:02 [PATCH v2] arm/acpi: Add Server Base System Architecture UART support Shanker Donthineni
2016-06-01 6:47 ` Wei Chen
2016-06-01 12:21 ` Shanker Donthineni
2016-06-01 13:49 ` Julien Grall
2016-06-01 15:14 ` Shanker Donthineni
2016-06-01 15:40 ` Julien Grall
2016-06-01 15:56 ` Andre Przywara
2016-06-01 16:18 ` Julien Grall [this message]
2016-06-02 14:51 ` Shanker Donthineni
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