linux-kernel - Re: [PATCH v3] tty: pl011: Work around QDF2400 E44 stuck BUSY bit

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Date:   Wed, 15 Feb 2017 12:07:54 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Christopher Covington <cov@...eaurora.org>,
        Jonathan Corbet <corbet@....net>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Peter Hurley <peter@...leysoftware.com>,
        Aleksey Makarov <aleksey.makarov@...aro.org>,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org, shankerd@...eaurora.org,
        timur@...eaurora.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Jiri Slaby <jslaby@...e.com>, linux-acpi@...r.kernel.org,
        linux-serial@...r.kernel.org, Mark Langsdorf <mlangsdo@...hat.com>,
        Mark Salter <msalter@...hat.com>, Jon Masters <jcm@...hat.com>,
        Neil Leeder <nleeder@...eaurora.org>, nd@....com
Subject: Re: [PATCH v3] tty: pl011: Work around QDF2400 E44 stuck BUSY bit

On Wed, Feb 15, 2017 at 07:50:27PM +0000, Mark Rutland wrote:
> On Wed, Feb 15, 2017 at 01:01:59PM -0500, Christopher Covington wrote:
> > The Qualcomm Datacenter Technologies QDF2400 family of SoCs contains a
> > custom (non-PrimeCell) implementation of the SBSA UART. Occasionally the
> > BUSY bit in the Flag Register gets stuck as 1, erratum 44 for both 2432v1
> > and 2400v1 SoCs.Checking that the Transmit FIFO Empty (TXFE) bit is 0,
> > instead of checking that the BUSY bit is 1, works around the issue.
> > 
> > To facilitate this substitution of flags and values, introduce
> > vendor-specific inversion of Feature Register bits when UART AMBA Port
> > (UAP) data is available. For the earlycon case, prior to UAP availability,
> > implement alternative putc and early_write functions.
> > 
> > Similar to what how ARMv8 ACPI PCI quirks are detected during MCFG parsing,
> > check the OEM fields of the Serial Port Console Redirection (SPCR) ACPI
> > table to determine if the current platform is known to be affected by the
> > erratum.
> > 
> > Signed-off-by: Christopher Covington <cov@...eaurora.org>
> > Acked-by: Russell King <rmk+kernel@...linux.org.uk>
> > ---
> > Since v2: Formatting and other improvements per Timur's suggestions
> > Due to known (although trivial) conflicts in silicon-errata.txt, based on
> > http://git.kernel.org/cgit/linux/kernel/git/arm64/linux.git/log/?h=for-next/core
> > ---
> >  Documentation/arm64/silicon-errata.txt |  2 ++
> >  drivers/acpi/spcr.c                    | 23 ++++++++++++
> >  drivers/tty/serial/amba-pl011.c        | 66 ++++++++++++++++++++++++++++++----
> >  3 files changed, 84 insertions(+), 7 deletions(-)
> > 
> > diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
> > index a71b8095dbd8..bc3d086bc624 100644
> > --- a/Documentation/arm64/silicon-errata.txt
> > +++ b/Documentation/arm64/silicon-errata.txt
> > @@ -68,3 +68,5 @@ stable kernels.
> >  |                |                 |                 |                             |
> >  | Qualcomm Tech. | Falkor v1       | E1003           | QCOM_FALKOR_ERRATUM_1003    |
> >  | Qualcomm Tech. | Falkor v1       | E1009           | QCOM_FALKOR_ERRATUM_1009    |
> > +| Qualcomm Tech. | QDF2432v1 UART  | SoC E44         | N/A                         |
> > +| Qualcomm Tech. | QDF2400v1 UART  | SoC E44         | N/A                         |
> > diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
> > index b8019c4c1d38..2b5d0fac81f0 100644
> > --- a/drivers/acpi/spcr.c
> > +++ b/drivers/acpi/spcr.c
> > @@ -16,6 +16,26 @@
> >  #include <linux/kernel.h>
> >  #include <linux/serial_core.h>
> >  
> > +/*
> > + * Some Qualcomm Datacenter Technologies SoCs have a defective UART BUSY bit.
> > + * Detect them by examining the OEM fields in the SPCR header, similiar to PCI
> > + * quirk detection in pci_mcfg.c.
> > + */
> > +static bool qdf2400_erratum_44_present(struct acpi_table_header *h)
> > +{
> > +	if (memcmp(h->oem_id, "QCOM  ", ACPI_OEM_ID_SIZE))
> > +		return false;
> > +
> > +	if (!memcmp(h->oem_table_id, "QDF2432 ", ACPI_OEM_TABLE_ID_SIZE))
> > +		return true;
> > +
> > +	if (!memcmp(h->oem_table_id, "QDF2400 ", ACPI_OEM_TABLE_ID_SIZE) &&
> > +			h->oem_revision == 0)
> > +		return true;
> > +
> > +	return false;
> > +}
> > +
> >  /**
> >   * parse_spcr() - parse ACPI SPCR table and add preferred console
> >   *
> > @@ -93,6 +113,9 @@ int __init parse_spcr(bool earlycon)
> >  		goto done;
> >  	}
> >  
> > +	if (qdf2400_erratum_44_present(&table->header))
> > +		uart = "qdf2400_e44";
> > +
> 
> This addresses my concern with using the MIDR; thanks for respinning
> this. FWIW:
> 
> Acked-by: Mark Rutland <mark.rutland@....com>
> 
> It might be best to split the silicon-errata doc into a separate patch.
> That can go via the arm64 tree without conflict whiel the driver patch
> can go via the tty tree.

Well, I can't take this as-is because I get conflicts in my tty tree
with the doc, and with the driver itself:

	checking file Documentation/arm64/silicon-errata.txt
	Hunk #1 FAILED at 68.
	1 out of 1 hunk FAILED
	checking file drivers/acpi/spcr.c
	checking file drivers/tty/serial/amba-pl011.c
	Hunk #5 FAILED at 2370.
	1 out of 8 hunks FAILED

I have no idea what the driver conflict is, what branch was this made
against?

thanks,

greg k-h