Messages in this thread | | | Date | Thu, 15 Jun 2023 09:50:52 +0530 | Subject | Re: [PATCH v8 6/9] usb: dwc3: qcom: Add multiport controller support for qcom wrapper | From | Krishna Kurapati PSSNV <> |
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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,
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