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Thu, 16 Jun 2022 15:01:46 -0700 (PDT) Received: from localhost ([2620:15c:11a:202:4ef5:7e3b:63ba:fc4]) by smtp.gmail.com with UTF8SMTPSA id d4-20020a62f804000000b00518c3307266sm2302542pfh.170.2022.06.16.15.01.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 16 Jun 2022 15:01:46 -0700 (PDT) Date: Thu, 16 Jun 2022 15:01:44 -0700 From: Matthias Kaehlcke To: Doug Anderson Cc: Greg Kroah-Hartman , Alan Stern , Rob Herring , Frank Rowand , Mathias Nyman , Felipe Balbi , Michal Simek , LKML , Krzysztof Kozlowski , Stephen Boyd , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Bastien Nocera , Peter Chen , Ravi Chandra Sadineni , Roger Quadros , Linux USB List , Geert Uytterhoeven , Souradeep Chowdhury Subject: Re: [PATCH v22 2/3] usb: misc: Add onboard_usb_hub driver Message-ID: References: <20220609192000.990763-1-mka@chromium.org> <20220609121838.v22.2.I7c9a1f1d6ced41dd8310e8a03da666a32364e790@changeid> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Thu, Jun 16, 2022 at 02:28:38PM -0700, Doug Anderson wrote: > Hi, > > On Thu, Jun 16, 2022 at 2:08 PM Matthias Kaehlcke wrote: > > > > On Thu, Jun 16, 2022 at 01:12:32PM -0700, Doug Anderson wrote: > > > Hi, > > > > > > On Wed, Jun 15, 2022 at 4:22 PM Matthias Kaehlcke wrote: > > > > > > > > > > +void onboard_hub_create_pdevs(struct usb_device *parent_hub, struct list_head *pdev_list) > > > > > > +{ > > > > > > + int i; > > > > > > + struct usb_hcd *hcd = bus_to_hcd(parent_hub->bus); > > > > > > + struct device_node *np, *npc; > > > > > > + struct platform_device *pdev = NULL; > > > > > > + struct pdev_list_entry *pdle; > > > > > > + > > > > > > + if (!parent_hub->dev.of_node) > > > > > > + return; > > > > > > + > > > > > > + for (i = 1; i <= parent_hub->maxchild; i++) { > > > > > > + np = usb_of_get_device_node(parent_hub, i); > > > > > > + if (!np) > > > > > > + continue; > > > > > > + > > > > > > + if (!of_is_onboard_usb_hub(np)) > > > > > > + goto node_put; > > > > > > + > > > > > > + npc = of_parse_phandle(np, "companion-hub", 0); > > > > > > + if (npc) { > > > > > > + /* > > > > > > + * Hubs with companions share the same platform device. > > > > > > + * Create the plaform device only for the hub that is > > > > > > + * connected to the primary HCD (directly or through > > > > > > + * other hubs). > > > > > > + */ > > > > > > + if (!usb_hcd_is_primary_hcd(hcd)) { > > > > > > + of_node_put(npc); > > > > > > + goto node_put; > > > > > > + } > > > > > > + > > > > > > + pdev = of_find_device_by_node(npc); > > > > > > + of_node_put(npc); > > > > > > + } else { > > > > > > + /* > > > > > > + * For root hubs this function can be called multiple times > > > > > > + * for the same root hub node (the HCD node). Make sure only > > > > > > + * one platform device is created for this hub. > > > > > > + */ > > > > > > + if (!parent_hub->parent && !usb_hcd_is_primary_hcd(hcd)) > > > > > > + goto node_put; > > > > > > > > > > I don't understand the "else" case above. What case exactly are we > > > > > handling again? This is when: > > > > > * the hub is presumably just a 2.0 hub since there is no companion. > > > > > * our parent is the root hub and the USB 2.0 hub we're looking at is > > > > > not the primary > > > > > > > > The 'else' case can be entered for hubs connected to a root hub or to another > > > > hub further down in the tree, but we bail out only for first level hubs. > > > > > > > > > ...but that doesn't make a lot of sense to me? I must have missed something... > > > > > > > > It's not super-obvious, this bit is important: "this function can be called > > > > multiple times for the same root hub node". For any first level hub we only > > > > create a pdev if this function is called on behalf of the primary HCD. That > > > > is also true of a hub connected to the secondary HCD. We only want to create > > > > one pdev and there is supposedly always a primary HCD. > > > > > > > > Maybe it would be slightly clearer if the function returned before the loop > > > > if this condition is met. > > > > > > I guess I'm still pretty confused. You say "For root hubs this > > > function can be called multiple times for the same root hub node". > > > Does that mean that the function will be called multiple times with > > > the same "parent_hub", or something else. > > > > It is called with a different "parent_hub", however for root hubs the > > DT node is the same for both root hubs (it's the DT node of the > > controller since there are no dedicated nodes for the root hubs). > > > > Just to make sure this isn't the source of the confusion: the root hubs > > are part of the USB controller, not 'external' hubs which are directly > > connected to the controller. I call the latter 'first level hubs'. > > > > > Unless it's called with the same "parent_hub" then it seems like if > > > the USB device has a device tree node and that device tree node is for > > > a onboard_usb_hub and there's no companion node then we _always_ want > > > to create the platform device, don't we? If it is called with the same > > > "parent_hub" then I'm confused how your test does something different > > > the first time the function is called vs. the 2nd. > > > > Let's use an adapted trogdor DT with only a USB 2.x hub as an example: > > > > usb_1_dwc3 { > > dr_mode = "host"; > > #address-cells = <1>; > > #size-cells = <0>; > > > > /* 2.x hub on port 1 */ > > usb_hub_2_x: hub@1 { > > compatible = "usbbda,5411"; > > reg = <1>; > > vdd-supply = <&pp3300_hub>; > > }; > > }; > > > > 1st call: the 'parent_hub' corresponds to the USB 3.x root hub of > > usb_1_dwc3, the DT node of the hub is 'usb_1_dwc3'. The function > > iterates over the ports, finds usb_hub_2_x, enters the else branch > > (no companion hub), checks that the function was called on behalf > > of the primary controller and creates the pdev. > > > > 2nd call: the 'parent_hub' corresponds to the USB 2.x root hub of > > usb_1_dwc3, the DT node of the hub is also 'usb_1_dwc3'. The function > > iterates over the ports, finds usb_hub_2_x, enters the else branch > > (no companion hub), sees that it is not called on behalf of the > > primary controller and does not create a second (unnecessary) pdev. > > > > Is it clearer now? > > Ah, I get it now! Sorry for being so dense... No worries, it's certainly not obvious and probably my commentary could have been clearer. > So like this: > > Root hubs (those hubs with no parent) are all created with the same > device_node, the one for the controller itself. We don't want to > iterate through the same children multiple times, so we bail right > away if we're detect that `parent_hub` is a root hub and we're not on > the primary HCD. yep > For all other cases the primary and secondary controllers have distinct > device_nodes. You probably mean that all non-root hubs have distinct nodes, so for these the function is only called once. > I guess in theory that test could go before the "companion-hub" test, > though I don't see any case where it truly matters... Yeah, I'm still wondering whether it would be slightly less confusing to bail before the loop (besides saving a few cycles), it would eliminate the conflation with the 'companion-hub' check.