Re: [PATCH v2 1/4] mfd: add viperboard driver

From: Lars Poeschel
Date: Thu Oct 18 2012 - 03:29:08 EST


On Tuesday 16 October 2012 at 12:58:48, Lars-Peter Clausen wrote:
> On 10/16/2012 11:43 AM, Lars Poeschel wrote:
> > On Tuesday 16 October 2012 at 10:40:26, Lars-Peter Clausen wrote:
> >> On 10/12/2012 04:34 PM, Lars Poeschel wrote:
> >> Btw. I'm wondering why is the extra platform device required? Can't you
> >> not just use the usb device as the parent device for the mfd cells?
> >
> > This is what I first did, but this does not work. You can read about my
> > first thoughts why this is not working here: (To sum it up: The device
> > is housed in an usb_device, not a platform_device and This usb_device
> > has no mfd_cell member.)
> >
> > https://lkml.org/lkml/2012/9/28/327
> >
> > As I got a bit more deeper I also noticed, that mfd_add_devices
> > (obviously) adds the devices "as childs" to the parent device.
> > mfd_remove_devices then removes ALL "child" devices from the parent, not
> > only those added by mfd_add_devices before. This does not work in the
> > case of the usb parent device, because it has other childs that the usb
> > layer added before (some endpoints and stuff). So I had to construct an
> > "empty" (in sense of childs) mock platform_device between the usb and
> > mfd.
>
> Ah, ok that makes sense. I was a bit confused, because there are other mfd
> drivers with for example i2c or spi devices as parents and these work fine,
> but I guess this is because non of them registers any additional child
> devices. I guess it makes sense to create a mfd cell device type and assign
> this type to newly created mfd cells and only unregister a device in
> mfd_remove_devices if it has the correct device type.
>
> E.g. something along the lines of:
>
>
> --- a/drivers/mfd/mfd-core.c
> +++ b/drivers/mfd/mfd-core.c
> @@ -21,6 +21,10 @@
> #include <linux/irqdomain.h>
> #include <linux/of.h>
>
> +static struct device_type mfd_device_type = {
> + .name = "mfd-cell",
> +};
> +
> int mfd_cell_enable(struct platform_device *pdev)
> {
> const struct mfd_cell *cell = mfd_get_cell(pdev);
> @@ -91,6 +95,7 @@ static int mfd_add_device(struct device *parent, int id,
> goto fail_device;
>
> pdev->dev.parent = parent;
> + pdev->dev.type = &mfd_device_type;
>
> if (parent->of_node && cell->of_compatible) {
> for_each_child_of_node(parent->of_node, np) {
> @@ -204,10 +209,16 @@ EXPORT_SYMBOL(mfd_add_devices);
>
> static int mfd_remove_devices_fn(struct device *dev, void *c)
> {
> - struct platform_device *pdev = to_platform_device(dev);
> - const struct mfd_cell *cell = mfd_get_cell(pdev);
> + struct platform_device *pdev;
> + const struct mfd_cell *cell;
> atomic_t **usage_count = c;
>
> + if (dev->type != &mfd_device_type)
> + return 0;
> +
> + pdev = to_platform_device(dev);
> + cell = mfd_get_cell(pdev);
> +
> /* find the base address of usage_count pointers (for freeing) */
> if (!*usage_count || (cell->usage_count < *usage_count))
> *usage_count = cell->usage_count;

I thought about this and I am not fully happy with it:
If we add the mfd devices to the usb_interface parent they are at the same
level in the device tree as the usb endpoints and stuff. I would consider this
logically wrong.
Is this something we should take care of ?
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