linux-kernel - Re: [linux-sunxi] Re: [PATCH 1/4] phy: sun4i-usb: support PHY0 on H3 in MUSB mode

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Date:   Fri, 20 Jan 2017 09:04:40 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Karsten Merker <merker@...ian.org>,
        Icenowy Zheng <icenowy@...c.xyz>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bin Liu <b-liu@...com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-sunxi@...glegroups.com" <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] Re: [PATCH 1/4] phy: sun4i-usb: support PHY0 on H3
 in MUSB mode

HI,

On 19-01-17 21:27, Karsten Merker wrote:
> On Thu, Jan 19, 2017 at 11:10:08PM +0800, Icenowy Zheng wrote:
>> 19.01.2017, 22:34, "Maxime Ripard" <maxime.ripard@...e-electrons.com>:
>>> On Wed, Jan 18, 2017 at 04:09:32AM +0800, Chen-Yu Tsai wrote:
>>>>  On Wed, Jan 18, 2017 at 4:06 AM, Maxime Ripard
>>>>  <maxime.ripard@...e-electrons.com> wrote:
>>>>  > On Wed, Jan 18, 2017 at 12:57:08AM +0800, Icenowy Zheng wrote:
>>>>  >> 17.01.2017, 16:06, "Maxime Ripard" <maxime.ripard@...e-electrons.com>:
>>>>  >> > On Tue, Jan 17, 2017 at 03:14:46AM +0800, Icenowy Zheng wrote:
>>>>  >> >> The PHY0 on H3 can be wired either to MUSB controller or OHCI/EHCI
>>>>  >> >> controller.
>>>>  >> >>
>>>>  >> >> The original driver wired it to OHCI/EHCI controller; however, as the
>>>>  >> >> code to use PHY0 as OHCI/EHCI is missing, it makes the PHY fully
>>>>  >> >> unusable.
>>>>  >> >>
>>>>  >> >> Rename the register (according to its function and the name in BSP
>>>>  >> >> driver), and remove the code which wires the PHY0 to OHCI/EHCI, as MUSB
>>>>  >> >> can support both peripheral and host mode (although the host mode of
>>>>  >> >> MUSB is buggy).
>>>>  >> >
>>>>  >> > Can you elaborate on that? What's wrong with it?
>>>>  >>
>>>>  >> The configuration is at bit 0 of register 0x20 in PHY.
>>>>  >>
>>>>  >> When the PHY is reseted, it defaults as MUSB mode.
>>>>  >>
>>>>  >> However, the original author of the H3 PHY code seems to be lack of
>>>>  >> this knowledge (He named it PHY_UNK_H3), and changed the PHY to HCI
>>>>  >> mode.
>>>>  >>
>>>>  >> I just removed the code that wires it to HCI mode, thus it will work
>>>>  >> in MUSB mode, with my sun8i-h3-musb patch.
>>>>  >
>>>>  > I have no idea what you mean by MUSB mode.
>>>>  >
>>>>  > Do you mean that the previous code was only working in host mode, and
>>>>  > now it only works in peripheral?
>>>>
>>>>  From what I understand, with the H3, Allwinner has put a mux
>>>>  in front of the MUSB controller. The mux can send the USB data
>>>>  to/from the MUSB controller, or a standard EHCI/OHCI pair.
>>>>  This register controls said mux.
>>>>
>>>>  This means we can use a proper USB host for host mode,
>>>>  instead of the limited support in MUSB.
>>>
>>> But musb can still operate as a host, right?
>>
>> Yes!
>
> Hello,
>
> I don't know how the MUSB implementation in the H3 behaves as I
> don't have any H3-based systems, but if it should happen to be
> similar to the one in the A31s, it probably isn't a full-fledged
> alternative to using an OHCI/EHCI controller.

You right it isn't which is why I suggested that the phy-sun4i-usb
code should set the mux to the OCHI/EHCI pair when the id pin
is pulled low (host-mode).

> From my practical experiments with the MUSB in the A31s in host
> mode I can report that I hadn't been able to get multiple HIDs
> (in my case keyboard and mouse) working at the same time.  The
> keyboard alone worked without problems, the mouse alone worked
> without problems, but when both were connected, only one of them
> worked.
>
> I had at that time talked to Hans de Goede about the problem and
> if I remenber correctly, he had mentioned that the MUSB has
> problems servicing more than one device that does interrupt
> transfers (as HIDs do).
>
> Hans, can you perhaps shed some light on this?

Everything you've said is correct, the MUSB can emulate a
host-controller, but it is not really one and when possible
should not be used as such.

Regards,

Hans