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[209.85.128.44]) by smtp.gmail.com with ESMTPSA id w12-20020a056402268c00b0042aaaf3f41csm2620158edd.4.2022.06.16.14.28.51 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 16 Jun 2022 14:28:51 -0700 (PDT) Received: by mail-wm1-f44.google.com with SMTP id m39-20020a05600c3b2700b0039c511ebbacso3433657wms.3 for ; Thu, 16 Jun 2022 14:28:51 -0700 (PDT) X-Received: by 2002:a05:600c:202:b0:39c:40de:ec19 with SMTP id 2-20020a05600c020200b0039c40deec19mr17409779wmi.29.1655414930918; Thu, 16 Jun 2022 14:28:50 -0700 (PDT) MIME-Version: 1.0 References: <20220609192000.990763-1-mka@chromium.org> <20220609121838.v22.2.I7c9a1f1d6ced41dd8310e8a03da666a32364e790@changeid> In-Reply-To: From: Doug Anderson Date: Thu, 16 Jun 2022 14:28:38 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v22 2/3] usb: misc: Add onboard_usb_hub driver To: Matthias Kaehlcke 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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... 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. For all other cases the primary and secondary controllers have distinct device_nodes. I guess in theory that test could go before the "companion-hub" test, though I don't see any case where it truly matters... -Doug