[Xen-devel] [PATCH 2/2] xen: Fix 16550 UART console for HP Moonshot (Aarch64) platform

[Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>]

    The console was not working on HP Moonshot (HPE Proliant Aarch64) because
    the UART registers were accessed as 8-bit aligned addresses. However,
    registers are 32-bit aligned for HP Moonshot.

    Since ACPI/SPCR table does not specify the register shift to be applied to 
the
    register offset, this patch implements an erratum to correctly set the 
register
    shift for HP Moonshot.

    Similar erratum was implemented in linux:

    commit 79a648328d2a604524a30523ca763fbeca0f70e3
    Author: Loc Ho <lho@xxxxxxx>
    Date:   Mon Jul 3 14:33:09 2017 -0700

        ACPI: SPCR: Workaround for APM X-Gene 8250 UART 32-alignment errata

        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@xxxxxxx>
        Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
        Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Signed-off-by: Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>
---
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>

 xen/drivers/char/ns16550.c | 42 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index b3f6d85..e716aba 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -1542,6 +1542,33 @@ DT_DEVICE_END
 #ifdef CONFIG_ACPI
 #include <xen/acpi.h>
 
+/*
+ * 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)
+{
+    bool xgene_8250 = false;
+
+    if ( tb->interface_type != ACPI_DBG2_16550_COMPATIBLE )
+        return false;
+
+    if ( memcmp(tb->header.oem_id, "APMC0D", ACPI_OEM_ID_SIZE) &&
+         memcmp(tb->header.oem_id, "HPE   ", ACPI_OEM_ID_SIZE) )
+        return false;
+
+    if ( !memcmp(tb->header.oem_table_id, "XGENESPC",
+         ACPI_OEM_TABLE_ID_SIZE) && tb->header.oem_revision == 0 )
+        xgene_8250 = true;
+
+    if ( !memcmp(tb->header.oem_table_id, "ProLiant",
+         ACPI_OEM_TABLE_ID_SIZE) && tb->header.oem_revision == 1 )
+        xgene_8250 = true;
+
+    return xgene_8250;
+}
+
 static int __init ns16550_acpi_uart_init(const void *data)
 {
     struct ns16550 *uart;
@@ -1568,9 +1595,20 @@ static int __init ns16550_acpi_uart_init(const void 
*data)
     uart->io_base = spcr->serial_port.address;
     uart->irq = spcr->interrupt;
     uart->reg_width = spcr->serial_port.bit_width/8;
-    uart->reg_shift = 0;
-    uart->io_size = UART_MAX_REG<<uart->reg_shift;
 
+    if ( xgene_8250_erratum_present(spcr) )
+    {
+        /*
+         * for xgene v1 and v2 the registers are 32-bit and so a
+         * register shift of 2 has to be applied to get the
+         * correct register offset.
+         */
+        uart->reg_shift = 2;
+    }
+    else
+        uart->reg_shift = 0;
+
+    uart->io_size = UART_MAX_REG<<uart->reg_shift;
     irq_set_type(spcr->interrupt, spcr->interrupt_type);
 
     uart->vuart.base_addr = uart->io_base;
-- 
2.7.4


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