Re: [PATCH v8 6/9] usb: dwc3: qcom: Add multiport controller support for qcom wrapper

Krishna Kurapati PSSNV
2023-06-07T19:51:31Z

On 6/7/2023 5:07 PM, Johan Hovold wrote:
> Hi Krishna,
>
> and sorry about the delay in following up on this. As usual, there are
> just way too many threads and this one in particular requires a bit of
> thought.
>
Hi Johan,

Thanks for taking the time out and reviewing the patches again.

> On Sat, May 20, 2023 at 11:18:52PM +0530, Krishna Kurapati PSSNV wrote:
>> On 5/17/2023 10:07 PM, Johan Hovold wrote:
>
>>> I don't think we should be adding more of these layering violations. A
>>> parent device driver has no business messing with the driver data for a
>>> child device which may or may not even have probed yet.
>>>
>>> I added a FIXME elsewhere in the driver about fixing up the current
>>> instances that have already snuck in (which in some sense is even worse
>>> by accessing driver data of a grandchild device).
>>>
>>> We really need to try sort this mess out and how to properly handle the
>>> interactions between these layers (e.g. glue, dwc3 core and xhci). This
>>> will likely involve adding callbacks from the child to the parent, for
>>> example, when the child is suspending.
>
>> I agree with you, but in this case I believe there is no other way we
>> can find the number of ports present. Unless its a dt property which
>> parent driver can access the child's of node and get the details. Like
>> done in v4 [1]. But it would be adding redundant data into DT as pointed
>> out by Rob and Krzysztof and so we removed these properties.
>
> So there at least two issues with this series:
>
> 1. accessing xhci registers from the dwc3 core
> 2. accessing driver data of a child device
>
> 1. The first part about accessing xhci registers goes against the clear
> separation between glue, core and xhci that Felipe tried to maintain.
>
> I'm not entirely against doing this from the core driver before
> registering the xhci platform device as the registers are unmapped
> afterwards. But if this is to be allowed, then the implementation should
> be shared with xhci rather than copied verbatim.
>
> The alternative that avoids this issue entirely could indeed be to
> simply count the number of PHYs described in DT as Rob initially
> suggested. Why would that not work?
>
The reason why I didn't want to read the Phy's from DT is explained in
[1]. I felt it makes the code unreadable and its very tricky to read the
phy's properly, so we decided we would initialize phy's for all ports
and if a phy is missing in DT, the corresponding member in
dwc->usbX_generic_phy[] would be NULL and any phy op on it would be a NOP.

Also as per Krzysztof suggestion on [2], we can add a compatible to read
number of phy's / ports present. This avoids accessing xhci members
atleast in driver core. But the layering violations would still be present.

> 2. The driver is already accessing driver data of the child device so
> arguably your series is not really making things much worse than they
> already are.
>
> I've just sent a couple of fixes to address some of the symptoms of
> this layering violation here:
>
> https://lore.kernel.org/lkml/20230607100540.31045-1-johan+linaro@kernel.org/
>

As you pointed out offline to me that using xhci event notifiers I
mentioned on [3], if it is not acceptable to use them as notifications
to check whether we are in host mode, I believe the only way would be to
use the patches you pushed in.

> Getting this fixed properly is going to take a bit of work, and
> depending on how your multiport wake up implementation is going to look
> like, adding support for multiport controllers may not make this much
> harder to address.
>
> So perhaps we can indeed merge support for multiport and then get back
> to cleaning this up.
So, you are referring to use the patches you pushed today as a partial
way to cleanup layering violations and merge multiport on top of it ? If
so, I am fine with it. I can rebase my changes on top of them.

[1]:
https://lore.kernel.org/all/4eb26a54-148b-942f-01c6-64e66541de8b@quicinc.com/
[2]:
https://lore.kernel.org/all/ca729f62-672e-d3de-4069-e2205c97e7d8@linaro.org/
[3]:
https://lore.kernel.org/all/37fd026e-ecb1-3584-19f3-f8c1e5a9d20a@quicinc.com/

Regards,
Krishna,