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Wed, 13 May 2020 15:45:33 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id C090CC43636; Wed, 13 May 2020 15:45:33 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: saiprakash.ranjan) by smtp.codeaurora.org (Postfix) with ESMTPSA id F05F6C433D2; Wed, 13 May 2020 15:45:32 +0000 (UTC) MIME-Version: 1.0 Date: Wed, 13 May 2020 21:15:32 +0530 From: Sai Prakash Ranjan To: Stephen Boyd Subject: Re: [PATCH] coresight: dynamic-replicator: Fix handling of multiple connections In-Reply-To: <158933457051.215346.13515171569230202840@swboyd.mtv.corp.google.com> References: <20200426143725.18116-1-saiprakash.ranjan@codeaurora.org> <47f6d51bfad0a0bf1553e101e6a2c8c9@codeaurora.org> <37b3749e-2363-0877-c318-9c334a5d1881@arm.com> <364049a30dc9d242ec611bf27a16a6c9@codeaurora.org> <158933457051.215346.13515171569230202840@swboyd.mtv.corp.google.com> Message-ID: <861f8ab0174d036cb1e49e34e4f81a92@codeaurora.org> X-Sender: saiprakash.ranjan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200513_084537_557859_3CC7536D X-CRM114-Status: GOOD ( 26.82 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mathieu Poirier , Suzuki K Poulose , linux-arm-msm@vger.kernel.org, Linux Kernel Mailing List , Russell King , linux-arm-kernel , Mike Leach Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-05-13 07:19, Stephen Boyd wrote: > Quoting Mike Leach (2020-05-12 14:52:33) >> HI Sai, >> >> On Tue, 12 May 2020 at 18:46, Sai Prakash Ranjan >> wrote: >> > >> > Hi Mike, >> > >> > On 2020-05-12 17:19, Mike Leach wrote: >> > [...] >> > >> > >> >> >> > >> >> Sorry for hurrying up and sending the patch - >> > >> >> https://lore.kernel.org/patchwork/patch/1239923/. >> > >> >> I will send v2 based on further feedbacks here or there. >> > >> >> >> > >> >>> >> > >> >>> 1) does this replicator part have a unique ID that differs from the >> > >> >>> standard ARM designed replicators? >> > >> >>> If so perhaps link the modification into this. (even if the part no >> > >> >>> in >> > >> >>> PIDR0/1 is the same the UCI should be different for a different >> > >> >>> implementation) >> > >> >>> >> > > I have reviewed the replicator driver, and compared to all the other CS >> > > drivers. >> > > This driver appears to be the only one that sets hardware values in >> > > probe() and expects them to remain in place on enable, and uses that >> > > state for programming decisions later, despite telling the PM >> > > infrastructure that it is clear to suspend the device. >> > > >> > > Now we have a system where the replicator hardware is behaving >> > > differently under the driver, but is it behaving unreasonably? >> > >> > Thanks for taking your time to review this. For new replicator behaving >> > unreasonably, I think the assumption that the context is not lost on >> > disabling clock is flawed since its implementation defined. Is such >> > assumption documented in any TRM? >> > >> >> Looking at the AMBA driver there is a comment there that AMBA does not >> lose state when clocks are removed. This is consistent with the AMBA >> protocol spec which states that AMBA slaves can only be accessed / >> read / write on various strobe signals, or state reset on PRESET >> signal, all timed by the rising edge of the bus clock. state changes >> are not permitted on clock events alone. Given this static nature of >> AMBA slaves then removing the clock should not have any effect. > > I believe the "clock" that is being used here is actually a software > message to the power manager hardware that the debug subsystem isn't > being used anymore. When nothing is requesting that it be enabled the > power manager turns off the power to the debug subsystem and then the > register context is lost. It shouldn't be a clock in the clk subsystem. > It should be a power domain and be attached to the amba devices in the > usual ways. Then the normal runtime PM semantics would follow. If amba > devices require a clk then we'll have to provide a dummy one that > doesn't do anything on this platform. > Note that there are 2 dynamic replicators and the behaviour is different only on one of the replicators(swao_replicator) which is in AOSS domain. I don't see how runtime PM would help us differentiate between them and handle PM differently for different replicators. Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel