From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sascha Hauer Subject: Re: [PATCH 0/5] Add Mediatek MT8173 subsystem clocks support Date: Mon, 8 Jun 2015 09:48:58 +0200 Message-ID: <20150608074858.GK6325@pengutronix.de> References: <1432192376-6712-1-git-send-email-jamesjj.liao@mediatek.com> <20150528132452.GI26575@pengutronix.de> <1432867649.15597.46.camel@mtksdaap41> <20150529062345.GY6325@pengutronix.de> <20150604210212.GM676@codeaurora.org> <1433468737.14416.7.camel@mtksdaap41> <20150606005912.GC29237@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150606005912.GC29237-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Stephen Boyd Cc: James Liao , Mike Turquette , srv_heupstream-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Henry Chen , Ricky Liang , Rob Herring , linux-mediatek-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Sascha Hauer , Matthias Brugger , Yingjoe Chen , Eddie Huang , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: devicetree@vger.kernel.org On Fri, Jun 05, 2015 at 05:59:12PM -0700, Stephen Boyd wrote: > On 06/05, James Liao wrote: > > Hi Stephen, > > > > On Thu, 2015-06-04 at 14:02 -0700, Stephen Boyd wrote: > > > On 05/29, Sascha Hauer wrote: > > > > Yes. I previously got the impression that the subsystem clocks are not > > > > directly associated to the larbs, but needed to be handled by the larb > > > > code due to some side effect. Now that I saw that the larbs are directly > > > > in the subsystem register space it all makes sense. > > > > > > > > Note that the way Mediatek SoCs are designed around sub modules is bit > > > > unusual and does not fit very well in the Linux directory structure. > > > > Normally SoCs have a single clocks controller which controls all clocks > > > > in the SoC. Then you often have a reset controller providing reset lines > > > > in the SoC. In this case it's clear that the clk driver goes to > > > > drivers/clk/, the reset controller driver to drivers/reset/. Mediatek > > > > SoCs instead have several blocks, each with its own clock and reset > > > > controller. Splitting each block up into parts in drivers/clk/ and > > > > drivers/reset/ leads to quite a code fragmentation. > > > > This is my opinion, it would be great to hear something from others. > > > > Matthias? I'd like to avoid running into a direction that is not > > > > acceptable in the end. > > > > > > We already have drivers registering clocks and resets under > > > drivers/clk, so it's not unheard of. An alternative solution is > > > to make child devices for the clock part and the reset part at > > > runtime in the toplevel driver for the vencsys device (don't do > > > any sort of DT description for this) and use regmap to mediate > > > the register accesses and locking. That way we can put the clk > > > driver in drivers/clk/, the reset driver in drivers/reset, etc. > > > so that logically related code is grouped. > > > > I have a question about the alternative way you mentioned. Currently > > clock providers and consumers describe what clocks they will provide / > > consume in device tree. If we don't describe vencsys clocks in device > > tree, how to get vencsys clocks for drivers that need to control them? > > > > Perhaps an example would be best. In DT we would have: > > vencsys: vencsys@10000 { > compatible = "mtk,vencsys"; > reg = <0x10000 0x1000>; > #clock-cells = <1>; > #reset-cells = <1>; > }; > > myconsumer@12000 { > compatible = "mtk,vencsys"; > reg = <0x12000 0x100>; > clocks = <&vencsys 10>; > clock-names = "core"; > }; > > (Or are the consumers only children of the subsystem? > It's not clear to me) > > And then in the mtk,vencsys driver we would create a platform > device named something like "mtk-vencsys-clk" and assign the > of_node of the device to be the of_node that is assigned to the > mtk,vencsys device. > > static int vencsys_probe(struct platform_device *pdev) > { > int ret; > struct device_node *np = pdev->dev.of_node; > struct platform_device *clk_pdev; > > clk_pdev = platform_device_alloc("mtk-vencsys-clk", -1); > clk_pdev->dev.of_node = of_node; > ret = platform_device_add(clk_pdev); > if (ret) > return ret; > } > > Then we could put a mtk-vencsys-clk driver in drivers/clk/ that > does the clk driver part... > > static int clk_vencsys_probe(struct platform_device *pdev) > { > int ret; > struct device_node *np = pdev->dev.of_node; > struct regmap *regmap; > > ret = of_clk_add_provider(np, of_clk_src_onecell_get, ..); > if (ret) > return ret; > > regmap = dev_get_regmap(pdev->dev.parent, NULL); > > } > > And similar things could be done for the reset driver. The problem I see with this approach is that we scatter the code for a otherwise simple driver over a bunch of directories. We would have drivers/clk/mediatek/vencsys.c drivers/reset/mediatek/vencsys.c drivers/soc/mediatek/vencsys.c The same must be added for vdecsys, imgsys and vencltsys. That will make 12 drivers and three maintainers for 12 registers. I think this will be a pain to maintain, hence my suggestion to put the vencsys code into a single file and not split this up into more subsystem specific files. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html