Best regards, Peter Chen > -----Original Message----- > From: Lucas Stach [mailto:l.stach@xxxxxxxxxxxxxx] > Sent: Wednesday, December 09, 2015 5:13 PM > To: Chen Peter-B29397 <Peter.Chen@xxxxxxxxxxxxx> > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>; Mark Rutland > <mark.rutland@xxxxxxx>; devicetree@xxxxxxxxxxxxxxx; festevam@xxxxxxxxx; > Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>; Paweł Moll <pawel.moll@xxxxxxx>; > Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>; linux-usb@xxxxxxxxxxxxxxx; > patryk@xxxxxxxxxxxx; Rob Herring <robh+dt@xxxxxxxxxx>; > stern@xxxxxxxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx; Shawn Guo > <shawnguo@xxxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Subject: Re: [PATCH 1/3] usb: misc: generic_onboard_hub: add generic > onboard USB HUB driver > > Am Mittwoch, den 09.12.2015, 17:00 +0800 schrieb Peter Chen: > > On Wed, Dec 09, 2015 at 09:57:40AM +0100, Lucas Stach wrote: > > > Am Mittwoch, den 09.12.2015, 16:50 +0800 schrieb Peter Chen: > > > > On Tue, Dec 08, 2015 at 08:36:00AM -0700, Mathieu Poirier wrote: > > > > > On 7 December 2015 at 18:37, Peter Chen <peter.chen@xxxxxxxxxxxxx> > wrote: > > > > > > + > > > > > > + if (dev->of_node) { > > > > > > + struct device_node *node = dev->of_node; > > > > > > + > > > > > > + hub_data->clk = devm_clk_get(dev, "external_clk"); > > > > > > + if (IS_ERR(hub_data->clk)) { > > > > > > + dev_dbg(dev, "Can't get external clock: %ld\n", > > > > > > + PTR_ERR(hub_data->clk)); > > > > > > + } > > > > > > > > > > Is the intended behaviour to keep going here event when there is > > > > > an error? Can the "hub_data" really work without a clock? > > > > > > > > Yes, some HUB may work with fixed 24M OSC at the board, but they > > > > need to reset through external IO, so the clock is not need at > > > > this case, but reset pin is mandatory. > > > > > > > If the hub always requires a clock it must not be optional. If you > > > have a fixed 24MHz clock on board add this to the DT as a > > > fixed-clock and use it as an input to the hub. > > > > > > > This fixed 24MHz clock may from a fixed crystal on board, it is always > > on, no software need to control it, imx51-bbg board is an example. > > > And that's wh it is a fixed-clock. Please look it up in the DT binding > documentation. Yes, I see similar things are described at [1], but why we need this additional entry at dts for this case, it is always on, no software is needed. [1] Documentation/devicetree/bindings/clock/clock-bindings.txt Peter ��.n��������+%������w��{.n����z�{��ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
