On 11/27/2012 09:22 PM, Andy Green wrote:
> On 11/28/2012 02:09 AM, the mail apparently from Alan Stern included:
>> On Wed, 28 Nov 2012, Andy Green wrote:
>>
>>>> Greg's advice was simply not to rely on pathnames in sysfs because they
>>>> aren't fixed in stone. That leaves plenty of other ways to approach
>>>> this problem.
>>>
>>> It's sage advice, but there is zero code provided in my patches that
>>> "relies on pathnames in sysfs".
>>
>> In your 1/5 patch, _device_path_generate() concatenates device name
>> strings, starting from a device root and separating elements with '/'
>> characters. Isn't that the same as a sysfs pathname?
>
> It's nothing to do with sysfs... yes some unrelated bits of sysfs also
> walk the device path. If we want to talk about how fragile the device
> path is as an id scheme over time we need to talk about likelihood of
> individual device names changing, not "sysfs". Anyway -->
>
>>>> Basically, what you want is for something related to device A (the
>>>> regulator or the GPIO) to happen whenever device B (the ehci-omap.0
>>>> platform device) is bound to a driver. The most straightforward way to
>>>> arrange this is for A's driver to have a callback that is invoked
>>>> whenever B is bound or unbound. The most straightforward way to
>>>> arrange _that_ is to allow each platform_device to have a list of
>>>> callbacks.
>>>
>>> Sorry I didn't really understand this proposal yet. You want "A", the
>>> regulator, driver to grow a callback function that gets called when the
>>> targeted platform_device ("B", ehci-omap.0) probe happens. Could you
>>> expand what the callback prototype or new members in the struct might
>>> look like? It's your tuple thing or we pass it an opaque pointer that
>>> is the struct regulator * or suchlike?
>>
>> Well, it won't be exactly the same as the tuple thing because no
>> strings will be involved, but it would be similar. The callback would
>> receive an opaque pointer (presumably to the regulator) and a device
>> pointer (the B device).
>
> OK. So I try to sketch it out iteractively to try to get in sync:
>
> device.h:
>
> enum asset_event {
> AE_PROBED,
> AE_REMOVED
> };
>
> struct device_asset {
> char *name; /* name of regulator, clock, etc */
> void *asset; /* regulator, clock, etc */
> int (*handler)(struct device *dev_owner, enum asset_event
> asset_event, struct device_asset *asset);
> };
>
> struct device {
> ...
> struct device_asset *assets;
> ...
> };
>
>
> drivers/base/dd.c | really_probe():
>
> ...
> struct device_asset *asset;
> ...
> asset = dev->assets;
> while (asset && asset->name) {
> if (asset->handler(dev, AE_PROBED, asset)) {
> /* clean up and bail */
> }
> asset++;
> }
>
> /* do probe */
> ...
>
>
> drivers/base/dd.c | __device_release_driver: (is this really the best
> place to oppose probe()?)
>
> ...
> struct device_asset *asset;
> ...
>
> /* call device ->remove() */
> ...
> asset = dev->assets;
> while (asset && asset->name) {
> asset->handler(dev, AE_REMOVED, asset);
> asset++;
> }
> ...
>
>
> board file:
>
> static struct regulator myreg = {
> .name = "mydevice-regulator",
> };
>
> static struct device_asset mydevice_assets[] = {
> {
> .name = "mydevice-regulator",
> .handler = regulator_default_asset_handler,
> },
> { }
> };
>
> static struct platform_device mydevice = {
> ...
> .dev = {
> .assets = mydevice_assets,
> },
> ...
> };
>
>From Pandaboard's point of view, is mydevice supposed to be referring to
ehci-omap, LAN95xx or something else?
Strictly speaking, the regulator doesn't belongs neither to ehci-omap
nor LAN95xx. It belongs to a power domain on the board. And user should
have control to switch it OFF when required without hampering operation
of ehci-omap, so that the other USB ports are still usable.
--
regards,
-roger
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