Date:   Wed, 20 Oct 2021 08:21:21 +0200
From:   Michal Simek <michal.simek@...inx.com>
To:     Fabrice Gasnier <fabrice.gasnier@...s.st.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Rob Herring <robh+dt@...nel.org>
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        Frank Rowand <frowand.list@...il.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Felipe Balbi <balbi@...nel.org>,
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Subject: Re: [PATCH v16 0/7] usb: misc: Add onboard_usb_hub driver



On 10/19/21 18:04, Fabrice Gasnier wrote:
> On 10/15/21 8:39 AM, Greg Kroah-Hartman wrote:
>> On Thu, Oct 14, 2021 at 02:38:55PM -0700, Doug Anderson wrote:
>>> Hi,
>>>
>>> On Tue, Sep 21, 2021 at 10:09 AM Matthias Kaehlcke <mka@...omium.org> wrote:
>>>>
>>>> Hi Greg,
>>>>
>>>> are there any actions pending or can this land in usb-testing?
>>>>
>>>> I confirmed that this series can be rebased on top of v5.15-rc2
>>>> without conflicts.
>>>
>>> I'm quite interested to know what the next action items are, too. This
>>> is one of the very few patches we have for trogdor (excluding MIPI
>>> camera, which is a long story) that we're carrying downstream, so I'm
>>> keenly interested in making sure it's unblocked (if, indeed, it's
>>> blocked on anything).
>>>
>>> If folks feel that this needs more review eyes before landing again
>>> then I'll try to find some time in the next week or two. If it's just
>>> waiting for the merge window to open/close so it can have maximal bake
>>> time, that's cool too. Please yell if there's something that I can do
>>> to help, though! :-)
>>
>> I would love more review-eyes on this please.
>>
> 
> Hi,
> 
> I noticed this series some time ago, and wanted to take a closer look.
> 
> The same issue this series address is seen on stm32 board for instance.
> (arch/arm/boot/dts/stm32mp15xx-dkx.dtsi). On board HUB (not described in
> the DT) is supplied by an always-on regulator.
> So it could could be interesting/useful to address the same case ,
> on stm32 boards, where USB2 (ehci-platform driver) is used currently.
> 
> I noticed a few things, especially on the dt-bindings. I've some
> questions here.
> 
> In this series, RTS5411 is used. The dt-bindings documents it as a child
> node of the USB controller. E.g.
> 
> &usb {
> 	usb_hub_2_0: hub@1 {
> 		...
> 	};
> 
> 	usb_hub_3_0: hub@2 {
> 	};
> }
> 
> I had a quick look at RTS5411 datasheet. It looks like there's an i2c
> interface too.
> - I guess the I2C interface isn't used in your case ?
>    (I haven't checked what it could be used for...)
> 
> In the stm32 boards (stm32mp15xx-dkx), there's an usb2514b chip
> - that also could be wired on I2C interface (0R mount option)
> - unused on stm32 boards by default
> 
> usb2514b chip already has a dt-bindings (with compatible), and a driver:
> - drivers/usb/misc/usb251xb.c
> - Documentation/devicetree/bindings/usb/usb251xb.txt
> 
> It is defined more as an i2c chip, so I'd expect it as an i2c child,
> e.g. like:
> 
> &i2c {
> 	usb2514b@2c {
> 		compatible = "microchip,usb2514b";
> 		...
> 	};
> };
> 
> 
> This way, I don't see how it could be used together with onboard_usb_hub
> driver ? (But I may have missed it)
> Is it possible to use a phandle, instead of a child node ?
> 
> However, in the stm32mp15xx-dkx case, i2c interface isn't wired/used by
> default. So obviously the i2c driver isn't used. In this case, could the
> "microchip,usb2514b" be listed in onboard_usb_hub driver ?
> (wouldn't it be redundant ?)
> 
> In this case it would be a child node of the usb DT node... Maybe that's
> more a question for Rob: would it be "legal" regarding existing
> dt-bindings ?

We wanted to upstream driver for microchip usb5744 and based on this 
thread with Rob

https://lore.kernel.org/all/CAL_JsqJZBbu+UXqUNdZwg-uv0PAsNg55026PTwhKr5wQtxCjVQ@mail.gmail.com/

the recommendation was to use i2c-bus link. And in our usb5744 case 
where usb hub has only one i2c address we just hardcoded it in the 
driver. I should be pushing this driver to xilinx soc tree soon if you 
want to take a look.

Thanks,
Michal

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