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SubjectRe: [PATCH v2 2/2] ACPI: SPCR: Workaround for APM X-Gene 8250 UART 32-alignment errata
On Mon, Jul 3, 2017 at 11:33 PM, Loc Ho <lho@apm.com> wrote:
> APM X-Gene verion 1 and 2 have an 8250 UART with its register
> aligned to 32-bit. In addition, the latest released BIOS
> encodes the access field as 8-bit access instead 32-bit access.
> This causes no console with ACPI boot as the console
> will not match X-Gene UART port due to the lack of mmio32
> option.
>
> Signed-off-by: Loc Ho <lho@apm.com>

Greg, Aleksey, any objections?

If not, I'll route this through the ACPI tree.

> ---
> drivers/acpi/spcr.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
> index 2905063..4ac3e06 100644
> --- a/drivers/acpi/spcr.c
> +++ b/drivers/acpi/spcr.c
> @@ -36,6 +36,26 @@ static bool qdf2400_erratum_44_present(struct acpi_table_header *h)
> return false;
> }
>
> +/*
> + * APM X-Gene v1 and v2 UART hardware is an 16550 like device but has its
> + * register aligned to 32-bit. In addition, the BIOS also encoded the
> + * access width to be 8 bits. This function detects this errata condition.
> + */
> +static bool xgene_8250_erratum_present(struct acpi_table_spcr *tb)
> +{
> + if (tb->interface_type != ACPI_DBG2_16550_COMPATIBLE)
> + return false;
> +
> + if (memcmp(tb->header.oem_id, "APMC0D", ACPI_OEM_ID_SIZE))
> + return false;
> +
> + if (!memcmp(tb->header.oem_table_id, "XGENESPC",
> + ACPI_OEM_TABLE_ID_SIZE) && tb->header.oem_revision == 0)
> + return true;
> +
> + return false;
> +}
> +
> /**
> * parse_spcr() - parse ACPI SPCR table and add preferred console
> *
> @@ -129,6 +149,8 @@ int __init parse_spcr(bool earlycon)
>
> if (qdf2400_erratum_44_present(&table->header))
> uart = "qdf2400_e44";
> + if (xgene_8250_erratum_present(table))
> + iotype = "mmio32";
>
> snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d", uart, iotype,
> table->serial_port.address, baud_rate);
> --
> 1.8.3.1
>

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