linux-kernel - Re: [PATCH v2 1/2] acpi, spcr: Make SPCR avialable to other architectures

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Message-ID: <20171214103027.GB697@e107981-ln.cambridge.arm.com>
Date:   Thu, 14 Dec 2017 10:30:27 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Timur Tabi <timur@...eaurora.org>
Cc:     Prarit Bhargava <prarit@...hat.com>, linux-acpi@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        linux-serial@...r.kernel.org, Bhupesh Sharma <bhsharma@...hat.com>,
        Lv Zheng <lv.zheng@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, graeme.gregory@...aro.org,
        mark.salter@...hat.com
Subject: Re: [PATCH v2 1/2] acpi, spcr: Make SPCR avialable to other
 architectures

On Wed, Dec 13, 2017 at 03:11:33PM -0600, Timur Tabi wrote:
> On 12/13/2017 06:45 AM, Lorenzo Pieralisi wrote:
> >>+/*
> >>+ * Erratum 44 for QDF2432v1 and QDF2400v1 SoCs describes the BUSY bit as
> >>+ * occasionally getting stuck as 1. To avoid the potential for a hang, check
> >>+ * TXFE == 0 instead of BUSY == 1. This may not be suitable for all UART
> >>+ * implementations, so only do so if an affected platform is detected in
> >>+ * acpi_parse_spcr().
> >>+ */
> >>+bool qdf2400_e44_present;
> >>+EXPORT_SYMBOL(qdf2400_e44_present);
> >
> >My eyes, this is horrible but it is not introduced by this patch. It
> >would have been much better if:
> >
> >drivers/tty/serial/amba-pl011.c
> >
> >parsed the SPCR table (again) to detect it instead of relying on this
> >horrible exported flag.
> 
> I didn't want to put any ACPI code in amba-pl011.c, so putting it in spcr.c
> made the most sense.  I agree the global variable is ugly.  If you have a
> better idea, I'm all ears.

I told you my idea. It could have been made easier by reusing the
ACPI_DECLARE_PROBE_ENTRY() mechanism.

> If it's any consolation, this erratum affects only 1.x silicon, which is
> technically pre-production (although a lot of people have them).  This
> work-around will eventually be reverted.

The sooner the better.

Lorenzo