Re: [PATCH 1/3] serial/imx: add device tree support

From: Mitch Bradley
Date: Tue Jun 21 2011 - 18:09:33 EST

On 6/21/2011 9:38 AM, Grant Likely wrote:
On Tue, Jun 21, 2011 at 1:35 PM, Mitch Bradley<wmb@xxxxxxxxxxxxx> wrote:
What is the problem with

serial0 = "/uart@7000c000";

Properties in the alias node are supposed to have string values.


Not sure I follow. Indeed, properties in the aliases node are string values.

Are you referring to how I was proposing some dtc syntax for
generating the alias strings?

The point is that if you refer to the node explicitly by its string name, the need for a label disappears and the problem of overriding a default alias disappears (assuming that a later redefinition of a property takes precedence over an earlier one, as is the OFW convention).


On 6/21/2011 9:13 AM, Grant Likely wrote:

On Tue, Jun 21, 2011 at 7:55 AM, Shawn Guo<shawn.guo@xxxxxxxxxxxxx>

Hi Grant,

I just gave a try to use aliases node for identify the device index.
Please take a look and let me know if it's what you expect.

Thanks Shawn. This is definitely on track. Comments below...

On Sun, Jun 19, 2011 at 03:30:02PM +0800, Shawn Guo wrote:

+#ifdef CONFIG_OF
+static int serial_imx_probe_dt(struct imx_port *sport,
+ struct platform_device *pdev)
+ struct device_node *node = pdev->dev.of_node;
+ const __be32 *line;
+ if (!node)
+ return -ENODEV;
+ line = of_get_property(node, "id", NULL);
+ if (!line)
+ return -ENODEV;
+ sport->port.line = be32_to_cpup(line) - 1;

Hmmm, I really would like to be rid of this. Instead, if uarts must
be enumerated, the driver should look for a /aliases/uart* property
that matches the of_node. Doing it that way is already established in
the OpenFirmware documentation, and it ensures there are no overlaps
in the global namespace.

I just gave one more try to avoid using 'aliases', and you gave a
'no' again. Now, I know how hard you are on this. Okay, I start
thinking about your suggestion seriously :)

We do need some infrastructure to make that easier though. Would you
have time to help put that together?

Ok, I will give it a try.

diff --git a/arch/arm/boot/dts/imx51-babbage.dts
index da0381a..f4a5c3c 100644
--- a/arch/arm/boot/dts/imx51-babbage.dts
+++ b/arch/arm/boot/dts/imx51-babbage.dts
@@ -18,6 +18,12 @@
compatible = "fsl,imx51-babbage", "fsl,imx51";
interrupt-parent =<&tzic>;

+ aliases {
+ serial0 =&uart0;
+ serial1 =&uart1;
+ serial2 =&uart2;
+ };

Hmmm. David Gibson had tossed out an idea of automatically generating
aliases from labels. It may be time to revisit that idea.

David, perhaps using this format for a label should turn it into an
alias (prefix label with an asterisk):

*thealias: i2c@12340000 { /*...*/ };

.... although that approach gets *really* hairy when considering that
different boards will want different enumeration. How would one
override an automatic alias defined by an included .dts file?

chosen {
bootargs = "console=ttymxc0,115200 root=/dev/mmcblk0p3
@@ -47,29 +53,29 @@
reg =<0x70000000 0x40000>;

- uart@7000c000 {
+ uart2: uart@7000c000 {
compatible = "fsl,imx51-uart",
reg =<0x7000c000 0x4000>;
interrupts =<33>;
id =<3>;
- fsl,has-rts-cts;
+ fsl,uart-has-rtscts;

- uart@73fbc000 {
+ uart0: uart@73fbc000 {
compatible = "fsl,imx51-uart", "fsl,imx21-uart";
reg =<0x73fbc000 0x4000>;
interrupts =<31>;
id =<1>;
- fsl,has-rts-cts;
+ fsl,uart-has-rtscts;

- uart@73fc0000 {
+ uart1: uart@73fc0000 {
compatible = "fsl,imx51-uart", "fsl,imx21-uart";
reg =<0x73fc0000 0x4000>;
interrupts =<32>;
id =<2>;
- fsl,has-rts-cts;
+ fsl,uart-has-rtscts;

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 632ebae..13df5d2 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -737,6 +737,37 @@ err0:

+ * of_get_device_index - Get device index by looking up "aliases"
+ * @np: Pointer to device node that asks for device index
+ * @name: The device alias without index number
+ *
+ * Returns the device index if find it, else returns -ENODEV.
+ */
+int of_get_device_index(struct device_node *np, const char *alias)
+ struct device_node *aliases = of_find_node_by_name(NULL,
+ struct property *prop;
+ char name[32];
+ int index = 0;
+ if (!aliases)
+ return -ENODEV;
+ while (1) {
+ snprintf(name, sizeof(name), "%s%d", alias, index);
+ prop = of_find_property(aliases, name, NULL);
+ if (!prop)
+ return -ENODEV;
+ if (np == of_find_node_by_path(prop->value))
+ break;
+ index++;
+ }

Rather than parsing the alias strings everytime, it would probably be
better to preprocess all the properties in the aliases node and create
a lookup table of alias->node references that can be walked quickly
and trivially.

Also, when obtaining an enumeration for a device, you'll need to be
careful about what number gets returned. If the node doesn't match a
given alias, but aliases do exist for other devices of like type, then
you need to be careful not to assign a number already assigned to
another device via an alias (this of course assumes the driver
supports dynamics enumeration, which many drivers will). It would be

\> +

+ return index;
* prom_add_property - Add a property to a node
int prom_add_property(struct device_node *np, struct property *prop)
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index da436e0..852668f 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1271,18 +1271,18 @@ static int serial_imx_probe_dt(struct imx_port
struct device_node *node = pdev->dev.of_node;
const struct of_device_id *of_id =
- const __be32 *line;
+ int line;

if (!node)
return -ENODEV;

- line = of_get_property(node, "id", NULL);
- if (!line)
+ line = of_get_device_index(node, "serial");
+ if (IS_ERR_VALUE(line))
return -ENODEV;

Personally, it an alias isn't present, then I'd dynamically assign a port

- sport->port.line = be32_to_cpup(line) - 1;
+ sport->port.line = line;

- if (of_get_property(node, "fsl,has-rts-cts", NULL))
+ if (of_get_property(node, "fsl,uart-has-rtscts", NULL))
sport->have_rtscts = 1;

if (of_get_property(node, "fsl,irda-mode", NULL))
diff --git a/include/linux/of.h b/include/linux/of.h
index bfc0ed1..3153752 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -213,6 +213,8 @@ extern int of_parse_phandles_with_args(struct
device_node *np,
const char *list_name, const char *cells_name, int index,
struct device_node **out_node, const void **out_args);

+extern int of_get_device_index(struct device_node *np, const char
extern int of_machine_is_compatible(const char *compat);

extern int prom_add_property(struct device_node* np, struct property*


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