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

On Fri, Sep 9, 2016 at 7:21 PM, Ben Dooks [off-list ref] wrote:

On 09/09/16 17:14, Martin Blumenstingl wrote:

quoted

On Fri, Sep 9, 2016 at 5:33 PM, Kevin Hilman [off-list ref] wrote:

quoted

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.

quoted

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.

okay, sounds reasonable - so we should try to get this scenario
supported through by the reset framework -> see my other mail.