linux-kernel - Re: [PATCH] ACPI: SPCR: Use access width to determine mmio usage

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Message-ID: <4e11bb2b-7cec-6a7b-ca2b-88be31a98b7d@redhat.com>
Date:   Sat, 6 May 2017 18:39:48 -0400
From:   Jon Masters <jcm@...hat.com>
To:     Jon Mason <jon.mason@...adcom.com>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Lv Zheng <lv.zheng@...el.com>
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        devel@...ica.org, bcm-kernel-feedback-list@...adcom.com,
        Loc Ho <lho@....com>
Subject: Re: [PATCH] ACPI: SPCR: Use access width to determine mmio usage

On 05/04/2017 11:05 AM, Jon Mason wrote:
> The current SPCR code does not check the access width of the mmio, and
> uses a default of 8bit register accesses.  This prevents devices that
> only do 16 or 32bit register accesses from working.  By simply checking
> this field and setting the mmio string appropriately, this issue can be
> corrected.  To prevent any legacy issues, the code will default to 8bit
> accesses if the value is anything but 16 or 32.

Thanks for this. Just as an FYI I've a running discussion with Microsoft
about defining additional UART subtypes in the DBG2 for special case
UARTs. Specifically, I want to address AppliedMicro's special 8250 dw IP
that also has a non-standard clock. At this time, there is general
agreement to use the access width for some cases rather than defining
yet more subtypes - so your patch is good.

Loc/Applied: please track this thread, incorporate feedback, and also
track the other general recent discussions of 8250 dw from this week.

Jon.

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