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Subject[PATCH v2 2/2] ACPI: SPCR: Workaround for APM X-Gene 8250 UART 32-alignment errata
Date
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>
---
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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