From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759156AbeD0UGK (ORCPT ); Fri, 27 Apr 2018 16:06:10 -0400 Received: from mail-pg0-f66.google.com ([74.125.83.66]:34008 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758945AbeD0UGH (ORCPT ); Fri, 27 Apr 2018 16:06:07 -0400 X-Google-Smtp-Source: AB8JxZocAEMXelUazRL/hnFZMEPgPlPIcTYbFqQ9cEjKOlMcUQbocyDvgFXiZ/h4acykiJyURpWpLQ== Date: Fri, 27 Apr 2018 13:06:05 -0700 From: Matthias Kaehlcke To: Lina Iyer Cc: andy.gross@linaro.org, david.brown@linaro.org, linux-arm-msm@vger.kernel.org, linux-soc@vger.kernel.org, rnayak@codeaurora.org, bjorn.andersson@linaro.org, linux-kernel@vger.kernel.org, sboyd@kernel.org, evgreen@chromium.org, dianders@chromium.org Subject: Re: [PATCH v6 05/10] drivers: qcom: rpmh-rsc: write sleep/wake requests to TCS Message-ID: <20180427200605.GJ243180@google.com> References: <20180419221635.17849-1-ilina@codeaurora.org> <20180419221635.17849-6-ilina@codeaurora.org> <20180425214111.GC243180@google.com> <20180427173943.GD6380@codeaurora.org> <20180427184017.GI243180@google.com> <20180427194559.GE6380@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180427194559.GE6380@codeaurora.org> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 27, 2018 at 01:45:59PM -0600, Lina Iyer wrote: > On Fri, Apr 27 2018 at 12:40 -0600, Matthias Kaehlcke wrote: > > On Fri, Apr 27, 2018 at 11:39:43AM -0600, Lina Iyer wrote: > > > On Wed, Apr 25 2018 at 15:41 -0600, Matthias Kaehlcke wrote: > > > > On Thu, Apr 19, 2018 at 04:16:30PM -0600, Lina Iyer wrote: > > > > > Sleep and wake requests are sent when the application processor > > > > > subsystem of the SoC is entering deep sleep states like in suspend. > > > > > These requests help lower the system power requirements when the > > > > > resources are not in use. > > > > > > > > > > Sleep and wake requests are written to the TCS slots but are not > > > > > triggered at the time of writing. The TCS are triggered by the firmware > > > > > after the last of the CPUs has executed its WFI. Since these requests > > > > > may come in different batches of requests, it is the job of this > > > > > controller driver to find and arrange the requests into the available > > > > > TCSes. > > > > > > > > > > Signed-off-by: Lina Iyer > > > > > Reviewed-by: Evan Green > > > > > --- > > > > > drivers/soc/qcom/rpmh-internal.h | 8 +++ > > > > > drivers/soc/qcom/rpmh-rsc.c | 120 +++++++++++++++++++++++++++++++ > > > > > 2 files changed, 128 insertions(+) > > > > > > > > > > diff --git a/drivers/soc/qcom/rpmh-internal.h b/drivers/soc/qcom/rpmh-internal.h > > > > > index d9a21726e568..6e19fe458c31 100644 > > > > > --- a/drivers/soc/qcom/rpmh-internal.h > > > > > +++ b/drivers/soc/qcom/rpmh-internal.h > > > > > > > > > > > > > > > > > +static int find_match(const struct tcs_group *tcs, const struct tcs_cmd *cmd, > > > > > + int len) > > > > > +{ > > > > > + int i, j; > > > > > + > > > > > + /* Check for already cached commands */ > > > > > + for_each_set_bit(i, tcs->slots, MAX_TCS_SLOTS) { > > > > > + for (j = 0; j < len; j++) { > > > > > + if (tcs->cmd_cache[i] != cmd[0].addr) { > > > > > > > > Shouldn't the condition be 'tcs->cmd_cache[i + j] != cmd[j].addr'? > > > > > > > Here, we are trying to find the first address from the request and its > > > position 'i' in the cmd_cache. > > > > > > > Otherwise the code below the following if branch will never be > > > > executed. Either the 'tcs->cmd_cache[i] != cmd[0].addr' branch isn't > > > > entered because the addresses match, or the addresses don't match > > > > and the inner loop is aborted after the first iteration. > > > > > > > > > + if (j == 0) > > > > > + break; > > > > > + WARN(tcs->cmd_cache[i + j] != cmd[j].addr, > > > > > + "Message does not match previous sequence.\n"); > > > We now check for the sequence using the iterator 'j' only after we have > > > found 'i' (the beginning of our request). > > > > > > I hope that helps clear the concern. > > > > It doesn't, maybe I'm just confused, the driver has a certain > > complexity and I don't claim to have a comprehensive understanding :) > > > > If I understand correctly find_match() is used to find a sequence of > > commands of length 'len' in the command cache. If that is correct I > > would expect it to do the following: > > > > 1. iterate through the commands in the command cache and find a > > command that matches the first command in the sequence > > > > 2. verify that the (len - 1) subsequent commands match those in the > > sequence, otherwise bail out > > > > If I'm not mistaken the current version of find_match() only checks > > that the first command exists. After that it happily increases the > > command index, but doesn't perform any checks (after finding the first > > command 'tcs->cmd_cache[i] != cmd[0].addr' remains false for the > > subsequent values of j). When j reaches (len - 1) the function > > returns the index of the first command in the cache, regardless of > > whether the other commands match or not. > > > Did you miss the check inside the WARN? > WARN(tcs->cmd_cache[i + j] != cmd[j].addr, My point is that this code is never reached, also regardless of the condition, the branch would always return -EINVAL. for (j = 0; j < len; j++) { if (tcs->cmd_cache[i] != cmd[0].addr) { if (j == 0) break; WARN(tcs->cmd_cache[i + j] != cmd[j].addr, "Message does not match previous sequence.\n"); return -EINVAL; } else if (j == len - 1) { return i; } } Let's single step through this, assuming the sequence of len=3 is in the cache: 1. j=0 2. (tcs->cmd_cache[i] != cmd[0].addr): false => branch with WARN + EINVAL not executed (good, this is the first command we are looking for) 3. (j == len - 1): false 4. j=1 5. (tcs->cmd_cache[i] != cmd[0].addr): false => branch with WARN + EINVAL not executed 6. (j == len - 1): false 7. j=2 8. (tcs->cmd_cache[i] != cmd[0].addr): false => branch with WARN + EINVAL not executed 9. (j == len - 1): true => return i Am I getting something wrong here?