[Xen-devel] [PATCH v2] ns16550: Add command line parsing adjustments

[Swapnil Paratey <swapnil.paratey@xxxxxxx>]

Add parsing options for reg_width and reg_shift in bootup command line
parameters. This adds flexibility in setting register values
for MMIO UART devices.

Increase length of opt_com1 and opt_com2 buffer to accommodate more
command line parameters.

eg. com1=115200,8n1,0x3f8,4 (legacy IO)
eg. com1=115200/3000000/4/2,8n1,0xfedc9000,4 (MMIO adjustments)

Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
Signed-off-by: Swapnil Paratey <swapnil.paratey@xxxxxxx>

---
Changed since v1:
  * Changed opt_com1 and opt_com2 array size to 64 (power of 2).
  * Added descriptions for reg_width and reg_shift in
    docs/misc/xen-command-line.markdown
  * Changed subject to ns16550 from 16550 for better tracking.
---
 docs/misc/xen-command-line.markdown | 11 ++++++++++-
 xen/drivers/char/ns16550.c          | 20 +++++++++++++++++---
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index 0138978..9ab7ead 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -291,7 +291,7 @@ Flag to indicate whether to probe for a CMOS Real Time 
Clock irrespective of
 ACPI indicating none to be there.
 
 ### com1,com2
-> `= 
<baud>[/<base-baud>][,[DPS][,[<io-base>|pci|amt][,[<irq>][,[<port-bdf>][,[<bridge-bdf>]]]]]]`
+> `= 
<baud>[/[<base-baud>][/[<reg-width>][/[<reg-shift>]]]][,DPS[,<io-base>[,<irq>[,<port-bdf>[,<bridge-bdf>]]]]]`
 
 Both option `com1` and `com2` follow the same format.
 
@@ -299,6 +299,15 @@ Both option `com1` and `com2` follow the same format.
   the bootloader or other earlier firmware has already set it up.
 * Optionally, the base baud rate (usually the highest baud rate the
   device can communicate at) can be specified.
+* `<reg-width>` is the access size, or width, for programming
+  the UART device registers.  Accepted values are 1 and 4 (bytes).
+  The UART device datasheet defines the register width to be used when
+  reading or writing the registers. This field is optional.
+  The default value is 1.
+* `<reg-shift>` is the number of bits to shift the register offset value
+  for programming the UART device registers. The UART device datasheet
+  defines the register shift needed to access the registers properly.
+  This field is optional. The default value is 0.
 * `DPS` represents the number of data bits, the parity, and the number
   of stop bits.
   * `D` is an integer between 5 and 8 for the number of data bits.
diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index 1da103a..0e80bce 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -33,14 +33,14 @@
 
 /*
  * Configure serial port with a string:
- *   
<baud>[/<base_baud>][,DPS[,<io-base>[,<irq>[,<port-bdf>[,<bridge-bdf>]]]]].
+ *   
<baud>[/[<base-baud>][/[<reg-width>][/[<reg-shift>]]]][,DPS[,<io-base>[,<irq>[,<port-bdf>[,<bridge-bdf>]]]]].
  * The tail of the string can be omitted if platform defaults are sufficient.
  * If the baud rate is pre-configured, perhaps by a bootloader, then 'auto'
  * can be specified in place of a numeric baud rate. Polled mode is specified
  * by requesting irq 0.
  */
-static char __initdata opt_com1[30] = "";
-static char __initdata opt_com2[30] = "";
+static char __initdata opt_com1[64] = "";
+static char __initdata opt_com2[64] = "";
 string_param("com1", opt_com1);
 string_param("com2", opt_com2);
 
@@ -1118,6 +1118,20 @@ static void __init ns16550_parse_port_config(
         uart->clock_hz = simple_strtoul(conf, &conf, 0) << 4;
     }
 
+    if ( *conf == '/' )
+    {
+        conf++;
+        if ( *conf != '/' && *conf != ',' )
+            uart->reg_width = simple_strtol(conf, &conf, 0);
+    }
+
+    if ( *conf == '/' )
+    {
+        conf++;
+        if ( *conf != '/' && *conf != ',' )
+            uart->reg_shift = simple_strtol(conf, &conf, 0);
+    }
+
     if ( *conf == ',' && *++conf != ',' )
     {
         uart->data_bits = simple_strtoul(conf, &conf, 10);
-- 
1.9.1


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