Re: [PATCH 4/7] phy: meson: add USB2 PHY support for Meson8b and GXBB

Ben Dooks
2016-09-09T17:21:14Z

On 09/09/16 17:14, Martin Blumenstingl wrote:
> On Fri, Sep 9, 2016 at 5:33 PM, Kevin Hilman <khilman@baylibre.com> wrote:
>> However, the problem with all of the solutions proposed (runtime PM ones
>> included) is that we're forcing a board-specific design issue (2 devices
>> sharing a reset line) into a driver that should not have any
>> board-specific assumptions in it.
>>
>> For example, if this driver is used on another platform where different
>> PHYs have different reset lines, then one of them (the unlucky one who
>> is not probed first) will never get reset. So any form of per-device
>> ref-counting is not a portable solution.
> maybe we should also consider Ben's solution: he played with the USB
> PHY on his Meson8b board. His approach was to have only one USB PHY
> driver instance which exposes two PHYs.
> The downside of this: the driver would have to know the offset of the
> PHYs (0x0 for the first PHY, 0x20 for the second), but we could handle
> the reset using runtime PM without any hacks.
>
> I checked the USB PHY reference driver: it seems that there will be a
> new USB PHY with the GXL/GXM SoCs.
> So maybe we could live with the assumption that the PHYs are at
> consecutive addresses.
>
>> I'm not sure yet how the reset framework is supposed to handle shared
>> reset lines, but that needs some investigation. I quick glance and it
>> seems that reset controllers can have shared lines, so that should be
>> investigated.
> unfortunately shared resets are not allowed to use reset_control_reset, see [0]
>
>
> [0] http://lxr.free-electrons.com/source/drivers/reset/core.c#L102

If we didn't have the shared reset, we'd have one of node per phy
and not have to have two sub-nodes... I don't think any other bits
of the PHY framework are shared.

--
Ben Dooks http://www.codethink.co.uk/
Senior Engineer Codethink - Providing Genius