From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D20E2C433EF for ; Wed, 9 Mar 2022 08:18:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230318AbiCIITR (ORCPT ); Wed, 9 Mar 2022 03:19:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40048 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229955AbiCIITR (ORCPT ); Wed, 9 Mar 2022 03:19:17 -0500 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E0A791CB1C for ; Wed, 9 Mar 2022 00:18:17 -0800 (PST) Received: from ptx.hi.pengutronix.de ([2001:67c:670:100:1d::c0]) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1nRrWQ-0000mv-AP; Wed, 09 Mar 2022 09:18:14 +0100 Received: from sha by ptx.hi.pengutronix.de with local (Exim 4.92) (envelope-from ) id 1nRrWM-0007ek-O8; Wed, 09 Mar 2022 09:18:10 +0100 Date: Wed, 9 Mar 2022 09:18:10 +0100 From: Sascha Hauer To: "zhangqing@rock-chips.com" Cc: =?utf-8?B?6Zer5a2d5Yab?= , Dmitry Osipenko , "robin.murphy" , =?utf-8?B?5byg5pm0?= , huangtao , devicetree , =?utf-8?B?5pON55Ge5p2w?= , Benjamin Gaignard , pgwipeout , hjc , dri-devel , =?utf-8?B?5p2o5Yev?= , linux-rockchip , Michael Riesch , kernel , Dmitry Osipenko , linux-arm-kernel Subject: Re: Re: [PATCH v7 10/24] drm/rockchip: dw_hdmi: Add support for hclk Message-ID: <20220309081810.GH405@pengutronix.de> References: <78207d97-b5a1-9792-8ec9-11fcf2e00370@gmail.com> <90c61299-f02c-607b-4734-7134852ef0a6@arm.com> <20220225131154.GE19585@pengutronix.de> <20220228141921.GN19585@pengutronix.de> <5184ecf2-8734-3121-cbbc-5dcfcf0d02f8@arm.com> <20220302112528.GV19585@pengutronix.de> <20220304142235.GL22780@pengutronix.de> <9ea0134e-aac7-60e1-5c58-ae31b4e1c422@collabora.com> <035f2dfd-bf35-abca-32bf-2be85cc88f8a@rock-chips.com> <20220309094139198367142@rock-chips.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220309094139198367142@rock-chips.com> X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-IRC: #ptxdist @freenode X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-Uptime: 08:57:51 up 88 days, 16:43, 82 users, load average: 0.00, 0.03, 0.08 User-Agent: Mutt/1.10.1 (2018-07-13) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c0 X-SA-Exim-Mail-From: sha@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: devicetree@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Hi Elaine, On Wed, Mar 09, 2022 at 09:41:39AM +0800, zhangqing@rock-chips.com wrote: > hi，all： > Let me explain the clock dependency： > From the clock tree, pclk_vo0 and hclk_vo0 are completely independent > clocks with different parent clocks and different clock frequencies。 > But the niu path is : > pclk_vo is dependent on hclk_vo, and the pclk_vo niu goes through  hclk_vo > niu. Thanks, this is the information we are looking for. What is "NIU" btw? I think this is even documented in the Reference Manual. With the right pointer I just found: > A part of niu clocks have a dependence on another niu clock in order to > sharing the internal bus. When these clocks are in use, another niu > clock must be opened, and cannot be gated. These clocks and the special > clock on which they are relied are as following: > > Clocks which have dependency The clock which can not be gated > ----------------------------------------------------------------- > ... > pclk_vo_niu, hclk_vo_s_niu hclk_vo_niu > ... > The clock tree and NIU bus paths are designed independently > So there are three solutions to this problem: > 1. DTS adds a reference to Hclk while referencing Pclk. > 2, The dependent clock is always on, such as HCLK_VO0, but this is not > friendly for the system power. > 3. Create a non-clock-tree reference. Clk-link, for example, we have an > implementation in our internal branch, but Upstream is not sure how to > push it. I thought about something similar. That would help us here and on i.MX we have a similar situation: We have one bit that switches multiple clocks. That as well cannot be designed properly in the clock framework currently, but could be modelled with a concept of linked clocks. Doing this sounds like quite a bit of work and discussion though, I don't really like having this as a dependency to mainline the VOP2 driver. I vote for 1. in that case, we could still ignore the hclk in dts later when we have linked clocks. Sascha -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |