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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E670DC04AB6 for ; Tue, 28 May 2019 15:20:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C510320665 for ; Tue, 28 May 2019 15:20:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727756AbfE1PU4 convert rfc822-to-8bit (ORCPT ); Tue, 28 May 2019 11:20:56 -0400 Received: from mo4-p01-ob.smtp.rzone.de ([85.215.255.51]:35232 "EHLO mo4-p01-ob.smtp.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726698AbfE1PUz (ORCPT ); Tue, 28 May 2019 11:20:55 -0400 X-RZG-AUTH: ":JGIXVUS7cutRB/49FwqZ7WcJeFKiMgPgp8VKxflSZ1P34KBj7wpz8NMGH/zvwDCv+Ds=" X-RZG-CLASS-ID: mo00 Received: from imac.fritz.box by smtp.strato.de (RZmta 44.18 DYNA|AUTH) with ESMTPSA id j04dc1v4SFKPrJe (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (curve secp521r1 with 521 ECDH bits, eq. 15360 bits RSA)) (Client did not present a certificate); Tue, 28 May 2019 17:20:25 +0200 (CEST) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Subject: Re: [PATCH] drm/omap: Migrate minimum FCK/PCK ratio from Kconfig to dts From: "H. Nikolaus Schaller" In-Reply-To: Date: Tue, 28 May 2019 17:20:25 +0200 Cc: Tomi Valkeinen , Linux-OMAP , Adam Ford , David Airlie , Daniel Vetter , Rob Herring , Mark Rutland , =?utf-8?Q?Beno=C3=AEt_Cousson?= , Tony Lindgren , dri-devel@lists.freedesktop.org, devicetree , Linux Kernel Mailing List Content-Transfer-Encoding: 8BIT Message-Id: References: <20190510194229.20628-1-aford173@gmail.com> To: Adam Ford X-Mailer: Apple Mail (2.3124) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Am 28.05.2019 um 17:09 schrieb Adam Ford : > > On Tue, May 28, 2019 at 4:11 AM Tomi Valkeinen wrote: >> >> Hi, >> >> On 10/05/2019 22:42, Adam Ford wrote: >>> Currently the source code is compiled using hard-coded values >>> from CONFIG_OMAP2_DSS_MIN_FCK_PER_PCK. This patch allows this >>> clock divider value to be moved to the device tree and be changed >>> without having to recompile the kernel. >>> >>> Signed-off-by: Adam Ford >> >> I understand why you want to do this, but I'm not sure it's a good idea. >> It's really something the driver should figure out, and if we add it to >> the DT, it effectively becomes an ABI. >> >> That said... I'm not sure how good of a job the driver could ever do, as >> it can't know the future scaling needs of the userspace at the time it >> is configuring the clock. And so, I'm not nacking this patch, but I >> don't feel very good about this patch... >> >> The setting also affects all outputs (exluding venc), which may not be >> what the user wants. Then again, I think this setting is really only >> needed on OMAP2 & 3, which have only a single output. But that's the >> same with the current kconfig option, of course. >> >> So, the current CONFIG_OMAP2_DSS_MIN_FCK_PER_PCK is an ugly hack, in my >> opinion, and moving it to DT makes it a worse hack =). But I don't have >> any good suggestions either. > > As it stands the Logic PD OMAP35 and AM37/DM37 boards (SOM-LV and > Torpedo) require this to be hard coded to 4 or it hangs during start. > This is the case for all versions 4.2+. I haven't tested it with > older stuff. Tony has a DM3730 Torpedo kit and reported the hanging > issue to me. I told him to set that value to 4 to make it not hang. > He asked that I move it to the DT to avoid custom kernels. I agree > it's a hack, but if it's create a customized defconfig file for 4 > boards or modify the device tree, it seems like the device tree > approach is less intrusive. Well, if this boards needs a factor 4 to be defined, it is IMHO 100 % correct to describe this in the DTS and nowhere else. Like minimum and maximum voltage of a regulator which is also very board specific. Unless it can be figured out automatically. If it turns out later that it can, I would assume the drivers can simply ignore the hint in the DTS? Just my 2cts without knowing details and having tested anything on our DM37 boards. BR, Nikolaus