Re: [PATCH 02/15] phy-sun4i-usb: Add a helper function to update the iscr register

[Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Hi,

On 09-03-15 22:47, Arnd Bergmann wrote:
> On Monday 09 March 2015 21:40:15 Hans de Goede wrote:
>> +void sun4i_usb_phy_update_iscr(struct phy *_phy, u32 clr, u32 set)
>> +{
>> +       struct sun4i_usb_phy *phy = phy_get_drvdata(_phy);
>> +       struct sun4i_usb_phy_data *data = to_sun4i_usb_phy_data(phy);
>> +       u32 iscr;
>> +
>> +       iscr = readl(data->base + REG_ISCR);
>> +       iscr &= ~clr;
>> +       iscr |= set;
>> +       writel(iscr, data->base + REG_ISCR);
>> +}
>> +EXPORT_SYMBOL(sun4i_usb_phy_update_iscr);
>> +
>>
>
> I would generally consider this a bad design. What is the purpose of
> calling sun4i_usb_phy_update_iscr()

There are 2 different use cases for this one is to enable the dataline
pull-ups at driver init and disable them at driver exit, this could /
should probably be moved to the phy_init / phy_exit code for the usb0 phy
removing the need to do this from within the sunxi musb glue.

The second use-case is more tricky, for some reasons Allwinner has decided
to not use the dedicated id-detect and vusb-sense pins of the phy they are
using (these pins are not routed to the outside).

Instead id-detect and vusb-sense are done through any $random gpio pins
(including non irq capable pins on some designs requiring polling).

But the musb-core still needs to know the status of the id and vbus pins,
and gets this from the usb0-phy iscr register, which reflects the status of
the not connected dedicated pins of the phy. The reason this can still
work at all is because the iscr register allows the user to override
whatever the not connected phy pins are seeing and forcing a value to
report to the musb core as id and vbus status.

This is done by these 2 functions in the musb sunxi glue:

static void sunxi_musb_force_id(struct musb *musb, u32 val)
{
         struct sunxi_glue *glue = dev_get_drvdata(musb->controller->parent);

         if (val)
                 val = SUNXI_ISCR_FORCE_ID_HIGH;
         else
                 val = SUNXI_ISCR_FORCE_ID_LOW;

         sun4i_usb_phy_update_iscr(glue->phy, SUNXI_ISCR_FORCE_ID_MASK, val);
}

static void sunxi_musb_force_vbus(struct musb *musb, u32 val)
{
         struct sunxi_glue *glue = dev_get_drvdata(musb->controller->parent);

         if (val)
                 val = SUNXI_ISCR_FORCE_VBUS_HIGH;
         else
                 val = SUNXI_ISCR_FORCE_VBUS_LOW;

         sun4i_usb_phy_update_iscr(glue->phy, SUNXI_ISCR_FORCE_VBUS_MASK, val);
}

I will happily admit that these 2 functions are a better API between the sunxi musb
glue and the sunxi usb phy driver. I started with the minimal sun4i_usb_phy_update_iscr
approach as I wanted to keep the API as small as possible, but having 2 functions like
the one above, which actually reflect what is happening would indeed be better.

Note that the polling of the pins cannot (easily) be moved into the phy driver for various
reasons:

1) It depends on dr_mode, the otg may be used in host only mode in which case there are no
pins at all.
2) the musb set_vbus callback needs access to the pins
3) When id changes some musb core state changes are necessary.

I'll respin the patch set to do things this way as soon as we've agreement on
your second point.

 > and why can't there be a high-level
> PHY API for this?

The current generic phy API seems to not have any bus specific methods, I know that
in the long run people want to get rid of struct usb_phy, so maybe we should consider
adding bus specific methods to the generic phy API for things like otg.

If we decide to add bus specific methods, then the question becomes if having

int phy_usb_set_id_detect(struct phy *phy, bool val);
int phy_usb_set_vbus_detect(struct phy *phy, bool val);

Functions in the generic phy API is a good idea, or if this is too sunxi specific,
I'm fine with doing this either way. If we want to go the generic phy route
I'll split this in 2 patches, one adding these 2 generic functions & phy-ops, and
1 doing the sunxi implementation.

If people believe this is too sunxi specific (I believe it is, but as said I'm
fine with doing this either way). I'll respin this patch to remove the too
generic sun4i_usb_phy_update_iscr function, and instead add these 2:

void sun4i_usb_phy_set_id_detect(struct phy *phy, bool val);
void sun4i_usb_phy_set_vbus_detect(struct phy *phy, bool val);

Regards,

Hans