From mboxrd@z Thu Jan 1 00:00:00 1970 From: Taniya Das Subject: Re: [PATCH v1] clk: qcom: lpass: Add CLK_IGNORE_UNUSED for lpass clocks Date: Tue, 22 Jan 2019 15:01:52 +0530 Message-ID: <72706ca8-91d0-7751-5f6b-1c2faf9483fb@codeaurora.org> References: <1545306385-31240-1-git-send-email-tdas@codeaurora.org> <154533989563.79149.10213938035592547726@swboyd.mtv.corp.google.com> <154689507747.15366.6553307032295093169@swboyd.mtv.corp.google.com> <154750471090.169631.5712250327468594228@swboyd.mtv.corp.google.com> <6ad2f27c-0afc-af6a-8198-679a88dcc2f9@codeaurora.org> <154783809872.169631.3437337484694848807@swboyd.mtv.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <154783809872.169631.3437337484694848807@swboyd.mtv.corp.google.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Stephen Boyd , Michael Turquette Cc: Andy Gross , David Brown , Rajendra Nayak , linux-arm-msm@vger.kernel.org, linux-soc@vger.kernel.org, linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org Hello Stephen, On 1/19/2019 12:31 AM, Stephen Boyd wrote: > Quoting Taniya Das (2019-01-17 03:19:22) >> >> >> On 1/15/2019 3:55 AM, Stephen Boyd wrote: >>> Quoting Taniya Das (2019-01-13 22:12:39) >>>> >>>> >>>> On 1/8/2019 2:34 AM, Stephen Boyd wrote: >>>>> >>>>> As far as I know, I'm not suggesting the use of CLK_IS_CRITICAL here. >>>>> But removing CLK_IS_CRITICAL and relying on some random bootloader >>>>> behavior also looks wrong. Can you clarify what's going on? >>>>> >>>> >>>> To enable LPASS clocks the requirement is to enable the GCC_LPASS_SWAY >>>> clock. >>>> 1) If the LPASS drivers are enabled/probed before the clock late init >>>> the client would take care to maintain the dependency to enable the >>>> GCC_LPASS_SWAY clock before enabling the LPASS clocks. >>>> >>>> 2) There could be a condition where the LPASS drivers would probe/init >>>> later the clock late_init. When the clock_late_init would try to access >>>> the LPASS clocks, since we cannot maintain the dependency this access >>>> would fail. To avoid this the earlier patch has made the GCC_LPASS_SWAY >>>> clock as CRITICAL. >>>> >>>> 3) Marking the GCC_LPASS_SWAY clock as CRITICAL has a issue, in the case >>>> where the LPASS subsystem would be restarted due to some critical >>>> failure on LPASS. Toggling the restart register of LPASS would clear the >>>> hardware state of this clock and thus the next access of the LPASS >>>> clocks would result in failure of the system. >>>> >>>> 4) To avoid issues happening in (2) and (3) all the LPASS clocks chould >>>> be safely marked as CLK_IGNORE_UNUSED. And lpass drivers would take care >>>> of the dependency to enable the required clocks. >>>> >>> >>> Ok, so why can't we enable/disable the lpass sway clk in the >>> prepare/unprepare phase of the lpass clk driver paths? Or why can't we >>> forcibly enable this lpass sway clk after the reset is deasserted? Which >>> clk controller is the reset part of? GCC or LPASS? >> >> It is part of Always On Subsystem. > > Ok. Is this merged upstream? > >> >>> >>> It still sounds like the LPASS clk driver isn't handling dependencies it >>> has on accessing registers, but maybe we can get away with not handling >>> the dependency still if we make the reset "do the right thing" and turn >>> the clk back on so it stays "critical". >>> >> >> This is a reset from hardware and it does not bring back the clock to >> the previous state and so we can not mark it "critical". I would submit >> the next series with comments updated. Please let me know in case you >> have any comments. >> >> > > Can we have the always on subsystem reset code go hit this clk enable > bit back on? There is no code, it is a reset from hardware. And also have the LPASS clk driver get this GCC sway clk > and enable it during probe? Maybe we need to get some sort of API in the > clk provider layer that can tell us that the clk state has changed now > and it needs to be restored. I haven't thought about it deeply but that > may be the best solution here. > Would it be possible to go about with the current patch and then have it updated with the possible solutions. -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation. --