From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Tanghe Subject: Re: [resend rfc v3] pwm: add BCM2835 PWM driver Date: Mon, 29 Sep 2014 15:37:50 +0200 Message-ID: <542960AE.1040200@thomasmore.be> References: <1398689686-30317-1-git-send-email-bart.tanghe@thomasmore.be> <20140825131908.GG4163@ulmo.nvidia.com> <5408395E.2030305@thomasmore.be> <54088008.9080200@wwwdotorg.org> <20140926071109.GA31106@ulmo> <54257C25.2000308@wwwdotorg.org> <20140929053311.GA12506@ulmo> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140929053311.GA12506@ulmo> Sender: linux-kernel-owner@vger.kernel.org To: Thierry Reding , Stephen Warren Cc: matt.porter@linaro.org, linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org, linux-rpi-kernel@lists.infradead.org List-Id: linux-pwm@vger.kernel.org On 2014-09-29 07:33, Thierry Reding wrote: > On Fri, Sep 26, 2014 at 08:45:57AM -0600, Stephen Warren wrote: >> On 09/26/2014 01:11 AM, Thierry Reding wrote: >>> On Thu, Sep 04, 2014 at 09:06:48AM -0600, Stephen Warren wrote: > [...] >>>> Oh dear. It sounds like we need at least some form of clock driver for the >>>> platform then. I still don't think there's complete documentation for the >>>> HW, even though a lot of register docs were published which presumably cover >>>> the clock HW? Equally, given that the VC firmware assumes it owns most of >>>> the HW, it seems best to manipulate the clocks through the firmware >>>> interface rather than directly touching the HW. Unfortunately, I don't >>>> believe there's any ABI guarantee on the firmware interface. Perhaps we can >>>> get one? >>> >>> Urgs... this VC firmware seems to be more of a headache that I thought >>> it was. How is this handled in other drivers? Surely PWM isn't the first >>> one that needs clocks? >> >> For the other clocks, I've set up dummy fixed-rate clocks in the DT and/or >> "clock driver" code to satisfy references by phandle or clock name >> respectively. Since the other drivers don't actually manipulate the clock >> rates etc., this is enough for the drivers. > > Given that this driver only queries the clock frequency adding a fixed- > rate clock to the device tree should work as well. Then the calls to > clk_prepare_enable() and clk_disable_unprepare() can still be added as > appropriate so that the driver doesn't need to change if a proper clock > driver ever gets added. > > Or am I missing anything? Perhaps the issue is that the default clock > rate for the PWM clock isn't usable? That would still not prevent the > driver from being merged. > > Thierry > The pwm clock is default unusable. To let the pwm clock run, It's necessary to change some clock registers. I've added the clk_prepare_enable and the clk_disable_unprepare functions. So the driver is able to work with a proper clock driver in the future. Bart