Best regards, Peter Chen
> -----Original Message----- > From: Lucas Stach [mailto:l.st...@pengutronix.de] > Sent: Wednesday, December 09, 2015 5:13 PM > To: Chen Peter-B29397 <peter.c...@freescale.com> > Cc: Mathieu Poirier <mathieu.poir...@linaro.org>; Mark Rutland > <mark.rutl...@arm.com>; devicet...@vger.kernel.org; feste...@gmail.com; > Philipp Zabel <p.za...@pengutronix.de>; Paweł Moll <pawel.m...@arm.com>; > Greg KH <gre...@linuxfoundation.org>; linux-usb@vger.kernel.org; > pat...@kowalczyk.ws; Rob Herring <robh...@kernel.org>; > st...@rowland.harvard.edu; ker...@pengutronix.de; Shawn Guo > <shawn...@kernel.org>; linux-arm-ker...@lists.infradead.org > 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.c...@freescale.com> > 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