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

From: Mitch Bradley <[email-masked]>
Date: Tue, 21 Jun 2011 18:08:56 -0400

On 6/21/2011 9:38 AM, Grant Likely wrote:
> On Tue, Jun 21, 2011 at 1:35 PM, Mitch Bradley<[email-masked]>  wrote:
>> What is the problem with
>>
>> aliases{
>>    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).

>
> g.
>
>>
>>
>> On 6/21/2011 9:13 AM, Grant Likely wrote:
>>>
>>> On Tue, Jun 21, 2011 at 7:55 AM, Shawn Guo<[email-masked]>
>>>   wrote:
>>>>
>>>> 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
>>>> b/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
>>>> rootwait";
>>>>         };
>>>> @@ -47,29 +53,29 @@
>>>>                         reg =<0x70000000 0x40000>;
>>>>                         ranges;
>>>>
>>>> -                       uart@7000c000 {
>>>> +                       uart2: uart@7000c000 {
>>>>                                 compatible = "fsl,imx51-uart",
>>>> "fsl,imx21-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:
>>>>   EXPORT_SYMBOL(of_parse_phandles_with_args);
>>>>
>>>>   /**
>>>> + *     of_get_device_index - Get device index by looking up "aliases"
>>>> node
>>>> + *     @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,
>>>> "aliases");
>>>> +       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;
>>>> +}
>>>> +EXPORT_SYMBOL(of_get_device_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
>>>> *sport,
>>>>         struct device_node *node = pdev->dev.of_node;
>>>>         const struct of_device_id *of_id =
>>>>                         of_match_device(imx_uart_dt_ids,&pdev->dev);
>>>> -       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
>>> id.
>>>
>>>>
>>>> -       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
>>>> *alias);
>>>> +
>>>>   extern int of_machine_is_compatible(const char *compat);
>>>>
>>>>   extern int prom_add_property(struct device_node* np, struct property*
>>>> prop);
>>>>
>>>> --
>>>> Regards,
>>>> Shawn
>>>>
>>>>
>>>
>>>
>>>
>>
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>
>
>