Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754226AbcDKLug (ORCPT ); Mon, 11 Apr 2016 07:50:36 -0400 Received: from bear.ext.ti.com ([192.94.94.41]:46931 "EHLO bear.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750756AbcDKLue (ORCPT ); Mon, 11 Apr 2016 07:50:34 -0400 Subject: Re: [PATCH v5 1/6] pwms: pwm-ti*: Get the clock from the PWMSS (parent) To: Paul Walmsley , "Franklin S Cooper Jr." References: <1457400224-24797-1-git-send-email-fcooper@ti.com> <1457400224-24797-2-git-send-email-fcooper@ti.com> <5703564C.7090700@ti.com> <5703A0C4.6010406@ti.com> CC: "Kristo, Tero" , , , , , , , , , , , , , , , From: Sekhar Nori Message-ID: <570B8F51.6040108@ti.com> Date: Mon, 11 Apr 2016 17:19:37 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3106 Lines: 70 On Monday 11 April 2016 02:21 AM, Paul Walmsley wrote: > Hi guys > > On Tue, 5 Apr 2016, Franklin S Cooper Jr. wrote: > >> On 04/05/2016 01:08 AM, Sekhar Nori wrote: >>> On Tuesday 08 March 2016 06:53 AM, Franklin S Cooper Jr wrote: >>>> The eCAP and ePWM doesn't have their own separate clocks. They simply >>>> utilize the clock provided directly by the PWMSS. Therefore, they simply >>>> need to grab a reference to their parent's clock. >>>> >>>> Signed-off-by: Franklin S Cooper Jr >>> >>> So this assumes that eCAP and eHRPWM are always under the PWMSS >>> umbrella. But on TI AM18x, thats not true. These IPs exist independently >>> and receive functional clock from PLL sysclk outputs. >>> >>>> --- >>>> drivers/pwm/pwm-tiecap.c | 2 +- >>>> drivers/pwm/pwm-tiehrpwm.c | 2 +- >>>> 2 files changed, 2 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/pwm/pwm-tiecap.c b/drivers/pwm/pwm-tiecap.c >>>> index 616af76..9418159 100644 >>>> --- a/drivers/pwm/pwm-tiecap.c >>>> +++ b/drivers/pwm/pwm-tiecap.c >>>> @@ -212,7 +212,7 @@ static int ecap_pwm_probe(struct platform_device *pdev) >>>> if (!pc) >>>> return -ENOMEM; >>>> >>>> - clk = devm_clk_get(&pdev->dev, "fck"); >>>> + clk = devm_clk_get(pdev->dev.parent, "fck"); >>> >>> Even keeping the AM18x usecase aside, this seems to be pushing too much >>> platform information into the driver. The "fck" is a valid connection id >>> for the eCAP IP. Whether its valid for the parent device too is not >>> something this driver should need to know. >>> >>> So it looks like what you need is for the clock hierarchy for the >>> platform to have clocks for eHRPWM and eCAP derived out of PWMSS clock? >> >> So I believe this is a question on if we want to hide the minor >> delta between AM18 vs AM335x, AM437x and AM57x/DRA7 in the driver >> or within the DT. >> >> Note that handling this by defining new clocks in DT will then >> result in older DTBs not working. I don't think its worth breaking >> backwards compatibility for AM335x and AM437x DTBs for fixing support >> for AM18 based SOCs. Especially since those SOCs haven't worked with >> this driver for several years. By handling things within the driver rather >> than DT we can atleast insure that we can get everything working while >> avoiding breaking backwards compatibility. > > I agree with Sekhar that we shouldn't embed this parent clock quirk > into the driver. > > Can you just define a new compatibility string such that the driver can be > written with no embedded integration quirks? Then add a workaround in the > driver that will use pdev->dev.parent for the old (deprecated) > compatibility string and log a warning to the kernel console that the DT > needs to be updated. Thanks Paul! Although not sure if adding a new compatible for the IP is the best way (since that would denote a different version of the IP). How about checking for parent clock iff clk_get() on own device fails and of_machine_is_compatible() matches the platforms where backward compatibility needs to be maintained? Thanks, Sekhar