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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=C5+Tj/x0seqvn19MWhPZoKn+VlDCEMR9Hc+Aq3tkzY8=; b=GEwWTWumjU+YU6i3GKUZCiLSUSQgl7F49ARapz4hOF0TYbgNAqpIj8k2P9c8x2Uq9q vvyEQVV1R3V2k8s/F5oZRag5gbC+oT2GlbPHnGxUAHxIO9VKHpxsAyezSR0Kson+xWlh lOD6fgh1ADIfUdXpi4YyrNl9y7fUvgYg653SVrMIZVas0cWK0OtgleEyYkFYwa5CJWe2 POT4LBP5eB7AWUF13Q33WLWmT/ZsYND0rCYz8Q6cGX102jPDRzIFlsgbP+mAFgRQ9M7o FxtV+ticqRyb+qrygLSWwZC/b56j5EJvlKtn1UnG2IM2PC6a6O0/IQVKEdiUi6AsIyRN 7kuA== X-Gm-Message-State: AGi0PuZ7OqwF3jGlpnheJEKyLQ87ch4Ms6USiUriDIKPuYwAKCVVO+vI WUD3VnBXudto/3EDy4Q8dfmSL87POXr/AWu1LnIsog== X-Google-Smtp-Source: APiQypJu3SjURBCeHG9XCeUMhTFUk1+T5l/kcmiOEHAKUxA8FMQScTewM/7d0CG0YpkFEyil0R95v+JbbO4tHHpx7Qg= X-Received: by 2002:aca:ab16:: with SMTP id u22mr2087293oie.133.1586274473098; Tue, 07 Apr 2020 08:47:53 -0700 (PDT) MIME-Version: 1.0 References: <20200331133346.372517-1-robert.foss@linaro.org> <20200331133346.372517-2-robert.foss@linaro.org> <20200401080705.j4goeqcqhoswhx4u@gilmour.lan> <20200403232736.GA6127@valkosipuli.retiisi.org.uk> <20200404093446.vuvwrhn5436h4d3s@gilmour.lan> <20200406083506.GE6127@valkosipuli.retiisi.org.uk> <20200407083647.4mocdl7aqa3x737q@gilmour.lan> <20200407123232.ktvaifhqntgzvkap@gilmour.lan> In-Reply-To: <20200407123232.ktvaifhqntgzvkap@gilmour.lan> From: Robert Foss Date: Tue, 7 Apr 2020 17:47:41 +0200 Message-ID: Subject: Re: [PATCH v6 1/3] media: dt-bindings: ov8856: Document YAML bindings To: Maxime Ripard X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200407_084754_611588_8E38EC5C X-CRM114-Status: GOOD ( 24.47 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , linux-kernel , Tomasz Figa , Sakari Ailus , Dongchun Zhu , Andy Shevchenko , Fabio Estevam , "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" , linux-media Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 7 Apr 2020 at 14:32, Maxime Ripard wrote: > > Hi Robert, > > On Tue, Apr 07, 2020 at 01:29:05PM +0200, Robert Foss wrote: > > On Tue, 7 Apr 2020 at 10:36, Maxime Ripard wrote: > > > On Mon, Apr 06, 2020 at 11:35:07AM +0300, Sakari Ailus wrote: > > > > > But that 19.2MHz is not a limitation of the device itself, it's a > > > > > limitation of our implementation, so we can instead implement > > > > > something equivalent in Linux using a clk_set_rate to 19.2MHz (to make > > > > > sure that our parent clock is configured at the right rate) and the > > > > > clk_get_rate and compare that to 19.2MHz (to make sure that it's not > > > > > been rounded too far apart from the frequency we expect). > > > > > > > > > > This is doing exactly the same thing, except that we don't encode our > > > > > implementation limitations in the DT, but in the driver instead. > > > > > > > > What I really wanted to say that a driver that doesn't get the clock > > > > frequency from DT but still sets that frequency is broken. > > > > > > > > This frequency is highly system specific, and in many cases only a certain > > > > frequency is usable, for a few reasons: On many SoCs, not all common > > > > frequencies can be used (e.g. 9,6 MHz, 19,2 MHz and 24 MHz; while others > > > > are being used as well), and then that frequency affects the usable CSI-2 > > > > bus frequencies directly --- and of those, only safe, known-good ones > > > > should be used. IOW, getting the external clock frequency wrong typically > > > > has an effect that that none of the known-good CSI-2 bus clock frequencies > > > > are available. > > > > > > So clock-frequency is not about the "Frequency of the xvclk clock in > > > Hertz", but the frequency at which that clock must run on this > > > particular SoC / board to be functional? > > > > > > If so, then yeah, we should definitely keep it, but the documentation > > > of the binding should be made clearer as well. > > > > Alright so, let me summarise the desired approach then. > > There's a separate discussion on the same topic here: > https://lore.kernel.org/linux-media/20200407122106.GD4751@pendragon.ideasonboard.com/ Thanks for the link. > > > ACPI: > > - Fetch the "clock-frequency" property > > - Verify it to be 19.2Mhz > > > > DT: > > - Fetch the "clock-frequency" property > > - Verify it to be 19.2Mhz > > - Get xvclk clock > > - Get xvclk clock rate > > - Verify xvclk clock rate to be 19.2Mhz > > The current status is that you should > 's/clock-frequency/link-frequencies/', and in order to replace > assigned-clock-rates, you'll want to have a clk_set_rate to 19.2MHz > between steps 3 and 4 Would we want to 's/clock-frequency/link-frequencies/' for ACPI too? I imagine that would cause some breakage. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel