From: Krishna Kurapati PSSNV <quic_kriskura@quicinc.com>
To: Thinh Nguyen <Thinh.Nguyen@synopsys.com>,
Johan Hovold <johan@kernel.org>,
Bjorn Andersson <andersson@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Philipp Zabel <p.zabel@pengutronix.de>,
Andy Gross <agross@kernel.org>,
Konrad Dybcio <konrad.dybcio@linaro.org>,
Rob Herring <robh+dt@kernel.org>,
"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
Felipe Balbi <balbi@kernel.org>,
"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"quic_pkondeti@quicinc.com" <quic_pkondeti@quicinc.com>,
"quic_ppratap@quicinc.com" <quic_ppratap@quicinc.com>,
"quic_wcheng@quicinc.com" <quic_wcheng@quicinc.com>,
"quic_jackp@quicinc.com" <quic_jackp@quicinc.com>,
"quic_harshq@quicinc.com" <quic_harshq@quicinc.com>,
"ahalaney@redhat.com" <ahalaney@redhat.com>
Subject: Re: [PATCH v8 6/9] usb: dwc3: qcom: Add multiport controller support for qcom wrapper
Date: Thu, 15 Jun 2023 09:50:52 +0530 [thread overview]
Message-ID: <acd46bb7-0708-d095-c3c6-53653f9e47d6@quicinc.com> (raw)
In-Reply-To: <20230609181602.ljxdchgzl7kzk73n@synopsys.com>
On 6/9/2023 11:46 PM, Thinh Nguyen wrote:
> On Fri, Jun 09, 2023, Johan Hovold wrote:
>> On Thu, Jun 08, 2023 at 05:57:23PM +0000, Thinh Nguyen wrote:
>>> On Thu, Jun 08, 2023, Krishna Kurapati PSSNV wrote:
>>>> On 6/8/2023 3:12 PM, Johan Hovold wrote:
>>>>> On Thu, Jun 08, 2023 at 01:21:02AM +0530, Krishna Kurapati PSSNV wrote:
>>>>>> On 6/7/2023 5:07 PM, Johan Hovold wrote:
>>>>>
>>>>>>> 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 core will just be looking at the HW capability registers and
>>> accessing the ports capability. Our programming guide also listed the
>>> host capability registers in its documentation. We're not driving the
>>> xhci controller here. We're initializing some of the core configs base
>>> on its capability.
>>>
>>> We're duplicating the logic here and not exactly doing it verbatim.
>>> Let's try not to share the whole xhci header where we should not have
>>> visibility over. Perhaps it makes sense in some other driver, but let's
>>> not do it here.
>>
>> The patch series even copied the kernel doc verbatim. This is just not
>> the way things are supposed to be done upstream. We share defines and
>> implementations all the time, but we should not be making copies of
>> them.
>
> We had some fixes to the kernel doc as it's incorrect description.
> Perhaps we can fully rewrite the kernel-doc if that what makes it
> better. We can share define implementations if they are meant to be
> shared. However, with the current way xhci header is implemented, it's
> not meant to be shared with dwc3. You agreed that we are violating this
> in some driver, but you're also insistent that we should not duplicate
> the logic to avoid this violation. Perhaps I'm not a maintainer here
> long enough to know some violation is better kept. If sharing the xhci
> header is what it takes to get this through, then fine.
>
>>
>>>>>>>
>>>>>>> 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?
>>>
>>> See below.
>>>
>>>>>>>
>>>>>> 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.
>>>>>
>>>>> That doesn't sound too convincing. Can't you just iterate over the PHYs
>>>>> described in DT and determine the maximum port number used for HS and
>>>>> SS?
>>>>>> 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.
>>>>>
>>>>> Yes, but if the information is already available in DT it's better to use
>>>>> it rather than re-encode it in the driver.
>>
>>>> Are you suggesting that we just do something like
>>>> num_ports = max( highest usb2 portnum, highest usb3 port num)
>>>
>>> Why do we want to do this? This makes num_ports ambiguous. Let's not
>>> sacrifice clarity for some lines of code.
>>
>> This is not about lines of code, but avoiding the bad practice of
>> copying code around and, to some degree, maintaining the separation
>> between the glue, core, and xhci which Felipe (perhaps mistakingly) has
>> fought for.
>
> We're talking about combining num_usb3_ports and num_usb2_ports here,
> what does that have to do with layer separation?
>
>>
>> If you just need to know how many PHYs you have in DT so that you can
>> iterate over that internal array, you can just look at the max index in
>> DT where the indexes are specified in the first place.
>>
>> Don't get hung up on the current variable names, those can be renamed to
>> match the implementation. Call it max_ports or whatever.
>
> It doesn't matter what variable name is given, it doesn't change the
> fact that this "num_ports" or "max_ports" obfuscated usb2 vs usb3 ports
> just for this specific implementation. So, don't do that.
>
>>
>>>> If so, incase the usb2 phy of quad port controller is missing in DT, we
>>>> would still read num_usb2_ports as 4 but the usb2_generic_phy[1] would be
>>>> NULL and any phy ops would still be NOP. But we would be getting rid of
>>>> reading the xhci registers compeltely in core driver.
>>>>
>>>> Thinh, Bjorn, can you also let us know your views on this.
>>>>
>>>> 1. Read:
>>>> num_usb3_ports = highest usb3 port index in DT
>>>> num_usb2_ports = max( highest usb2 port index, num_usb3_ports)
>>>>
>>>> 2. Read the same by parsing xhci registers as done in recent versions of
>>>> this series.
>>>
>>> DT is not reliable to get this info. As noted, the DT may skip some
>>> ports and still be fine. However, the driver doesn't know which port
>>> reflects which port config index without the exact port count.
>>
>> That's not correct. DT provides the port indexes already, for example:
>>
>> phy-names = "usb2-port0", "usb3-port0",
>> "usb2-port1", "usb3-port1",
>> "usb2-port2",
>> "usb2-port3";
>>
>> So if you just need this to iterate over the PHYs all the information
>> needed is here.
>>
>> If you need to access ports which do not have a PHY described in DT,
>> then this is not going to suffice, but I have not seen anyone claim that
>> that is needed yet.
>
> Perhaps I misunderstand the conversation. However, there isn't a method
> that everyone's agree on yet regarding DT [*]. Perhaps this indicates it
> may not be the best approach. You can resume the conversation if you
> want to:
>
> [*] https://lore.kernel.org/linux-usb/9671cade-1820-22e1-9db9-5c9836414908@quicinc.com/#t
>
>>
>>> More importantly, the host controller that lives on the PCI bus will not
>>> use DT. This can be useful for some re-configurations if the controller
>>> is a PCI device and that goes through the dwc3 code path.
>>
>> Ok, this is a bit hand wavy, but if this ever turns out to be needed it
>> can also be implemented then.
>
> What does hand wavy mean? We have case where it's useful outside of
> this, and it would be useful for PCI device too:
>
> https://lore.kernel.org/linux-usb/20230517233218.rjfmvptrexgkpam3@synopsys.com/
>
>>
>> Or just generalise the xhci implementation for parsing these registers
>> and reuse that from the start. (As a bonus you'd shrink the kernel text
>> size by getting rid of that iffy inline implementation.)
>>
>
> I don't like the iffy inline function either. We changed that here. To
> rework the xhci header and define its global header seems a bit
> excessive just for dwc3 to get the port capability. Regardless, as I've
> said, if we _must_, perhaps we can just import xhci-ext-caps.h instead
> of the whole xhci.h.
Hi Thinh, Johan,
How about we add compatible data indicating the number of usb2/usb3
ports. That way we needn't parse the DT or read xhci registers atleast
as a temporary solution to unblock other patches. Once this series is
merged, we can get back to fixing the port count calculation. Does it
seem fine ?
Regards,
Krishna,
next prev parent reply other threads:[~2023-06-15 4:21 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-14 5:49 [PATCH v8 0/9] Add multiport support for DWC3 controllers Krishna Kurapati
2023-05-14 5:49 ` [PATCH v8 1/9] dt-bindings: usb: qcom,dwc3: Add bindings for SC8280 Multiport Krishna Kurapati
2023-05-14 9:46 ` Krzysztof Kozlowski
2023-05-16 10:59 ` Johan Hovold
2023-05-17 11:10 ` Krishna Kurapati PSSNV
2023-05-17 11:44 ` Johan Hovold
2023-05-17 12:19 ` Krishna Kurapati PSSNV
2023-05-17 12:55 ` Johan Hovold
2023-05-14 5:49 ` [PATCH v8 2/9] dt-bindings: usb: Add bindings for multiport properties on DWC3 controller Krishna Kurapati
2023-05-14 5:49 ` [PATCH v8 3/9] usb: dwc3: core: Access XHCI address space temporarily to read port info Krishna Kurapati
2023-05-15 21:08 ` Bjorn Andersson
2023-05-16 2:12 ` Krishna Kurapati PSSNV
2023-05-16 22:39 ` Thinh Nguyen
2023-05-16 12:11 ` Johan Hovold
2023-05-16 15:02 ` Krishna Kurapati PSSNV
2023-05-17 3:10 ` Krishna Kurapati PSSNV
2023-05-17 3:21 ` Thinh Nguyen
2023-05-17 7:46 ` Johan Hovold
2023-05-17 23:21 ` Thinh Nguyen
2023-06-07 11:56 ` Johan Hovold
2023-05-17 7:35 ` Johan Hovold
2023-05-17 12:21 ` Krishna Kurapati PSSNV
2023-05-17 15:10 ` Johan Hovold
2023-05-14 5:49 ` [PATCH v8 4/9] usb: dwc3: core: Skip setting event buffers for host only controllers Krishna Kurapati
2023-05-15 21:19 ` Bjorn Andersson
2023-05-16 12:17 ` Johan Hovold
2023-05-16 14:28 ` Krishna Kurapati PSSNV
2023-05-14 5:49 ` [PATCH v8 5/9] usb: dwc3: core: Refactor PHY logic to support Multiport Controller Krishna Kurapati
2023-05-15 21:47 ` Bjorn Andersson
2023-05-16 2:31 ` Krishna Kurapati PSSNV
2023-05-17 16:17 ` Johan Hovold
2023-05-14 5:49 ` [PATCH v8 6/9] usb: dwc3: qcom: Add multiport controller support for qcom wrapper Krishna Kurapati
2023-05-15 22:27 ` Bjorn Andersson
2023-05-16 2:19 ` Krishna Kurapati PSSNV
2023-05-17 16:37 ` Johan Hovold
2023-05-20 17:48 ` Krishna Kurapati PSSNV
2023-06-07 11:37 ` Johan Hovold
2023-06-07 19:51 ` Krishna Kurapati PSSNV
2023-06-08 9:42 ` Johan Hovold
2023-06-08 15:23 ` Krishna Kurapati PSSNV
2023-06-08 17:57 ` Thinh Nguyen
2023-06-09 8:18 ` Johan Hovold
2023-06-09 18:16 ` Thinh Nguyen
2023-06-15 4:20 ` Krishna Kurapati PSSNV [this message]
2023-06-15 21:08 ` Thinh Nguyen
2023-06-21 7:38 ` Johan Hovold
2023-06-22 4:39 ` Krishna Kurapati PSSNV
2023-06-21 7:34 ` Johan Hovold
2023-06-22 22:41 ` Thinh Nguyen
2023-05-26 2:55 ` Bjorn Andersson
2023-05-26 15:25 ` Krishna Kurapati PSSNV
2023-06-07 11:44 ` Johan Hovold
2023-06-07 19:55 ` Krishna Kurapati PSSNV
2023-06-08 9:44 ` Johan Hovold
2023-06-07 12:16 ` Johan Hovold
2023-06-27 15:43 ` Johan Hovold
2023-07-02 19:05 ` Krishna Kurapati PSSNV
2023-07-14 9:00 ` Johan Hovold
2023-07-14 10:38 ` Krishna Kurapati PSSNV
2023-07-21 11:16 ` Johan Hovold
2023-07-21 12:10 ` Konrad Dybcio
2023-07-21 12:54 ` Johan Hovold
2023-08-11 16:48 ` Konrad Dybcio
2023-08-12 8:58 ` Krishna Kurapati PSSNV
2023-05-14 5:49 ` [PATCH v8 7/9] arm64: dts: qcom: sc8280xp: Add multiport controller node for SC8280 Krishna Kurapati
2023-05-15 14:26 ` Johan Hovold
2023-05-15 15:32 ` Krishna Kurapati PSSNV
2023-05-16 10:54 ` Johan Hovold
2023-05-16 14:24 ` Krishna Kurapati PSSNV
2023-05-16 14:42 ` Johan Hovold
2023-05-16 14:44 ` Krishna Kurapati PSSNV
2023-05-14 5:49 ` [PATCH v8 8/9] arm64: dts: qcom: sa8295p: Enable tertiary controller and its 4 USB ports Krishna Kurapati
2023-05-14 5:49 ` [PATCH v8 9/9] arm64: dts: qcom: sa8540-ride: Enable first port of tertiary usb controller Krishna Kurapati
2023-05-15 2:40 ` [PATCH v8 0/9] Add multiport support for DWC3 controllers Bjorn Andersson
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