On Wed, Jun 21, 2023, Johan Hovold wrote: > Hi Thinh, > > and sorry about the late reply. Was on holiday last week. > > On Fri, Jun 09, 2023 at 06:16:13PM +0000, 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. > > No, this is an example of why you should not copy code (and docs) > around, for example, so you don't have to fix the same bug (or typo) in > multiple places. > > > 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. > > Just because no-one has used these outside of xhci today, doesn't mean > that you should copy the defines once they are needed outside that > driver. > > And in fact, they are used outside of the xhci driver proper already > today, only that people took the lazy approach and shared the inline > helper for that. > > > > > > > > > > > > > > > > > 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? > > I mentioned this is as an alternative if you're are hell-bent on not > reusing the xhci register defines and parsing code. > > > > 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. > > Ok, then make sure you reuse the xhci implementation for that then. > > > > > > 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://urldefense.com/v3/__https://lore.kernel.org/linux-usb/9671cade-1820-22e1-9db9-5c9836414908@xxxxxxxxxxx/*t__;Iw!!A4F2R9G_pg!btc_fkrnAm1eFG5c5V0bWMnPnq4yvFyza1nDRJE8mPvSSrYIyxkUxjAARU51cRsoo2n0eLwTGt_SYvnQOaQ$ > > This was the approach suggested by Rob, the DT maintainer, in that very > thread IIRC. > > > > > 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://urldefense.com/v3/__https://lore.kernel.org/linux-usb/20230517233218.rjfmvptrexgkpam3@xxxxxxxxxxxx/__;!!A4F2R9G_pg!btc_fkrnAm1eFG5c5V0bWMnPnq4yvFyza1nDRJE8mPvSSrYIyxkUxjAARU51cRsoo2n0eLwTGt_SqPJ_Tn0$ > > Hand-wavy as in lacking detail which makes it hard to evaluate the > argument. > > > > 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. > > No one said anything about importing the whole of xhci.h. > This was how it was originally done in the earlier version of the series. Perhaps that's why I was against it. It looks wrong for dwc3 to know about xhci_hcd structure. Thanks, Thinh
