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[68.147.8.254]) by smtp.gmail.com with ESMTPSA id v6sm3292828pgf.55.2020.08.27.13.44.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Aug 2020 13:44:28 -0700 (PDT) Date: Thu, 27 Aug 2020 14:44:26 -0600 From: Mathieu Poirier To: Qi Liu Cc: gregkh@linuxfoundation.org, suzuki.poulose@arm.com, mike.leach@linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, coresight@lists.linaro.org Subject: Re: [RFC PATCH v2] coresight: etm4x: Modify core-commit of cpu to avoid the overflow of HiSilicon ETM Message-ID: <20200827204426.GD22307@xps15> References: <1597824397-29894-1-git-send-email-liuqi115@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1597824397-29894-1-git-send-email-liuqi115@huawei.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Liu, On Wed, Aug 19, 2020 at 04:06:37PM +0800, Qi Liu wrote: > When too much trace information is generated on-chip, the ETM will > overflow, and cause data loss. This is a common phenomenon on ETM > devices. > > But sometimes we do not want to lose performance trace data, so we > suppress the speed of instructions sent from CPU core to ETM to > avoid the overflow of ETM. > > Signed-off-by: Qi Liu > --- > > Changes since v1: > - ETM on HiSilicon Hip09 platform supports backpressure, so does > not need to modify core commit. > > drivers/hwtracing/coresight/coresight-etm4x.c | 43 +++++++++++++++++++++++++++ > 1 file changed, 43 insertions(+) > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c > index 7797a57..7641f89 100644 > --- a/drivers/hwtracing/coresight/coresight-etm4x.c > +++ b/drivers/hwtracing/coresight/coresight-etm4x.c > @@ -43,6 +43,10 @@ MODULE_PARM_DESC(boot_enable, "Enable tracing on boot"); > #define PARAM_PM_SAVE_NEVER 1 /* never save any state */ > #define PARAM_PM_SAVE_SELF_HOSTED 2 /* save self-hosted state only */ > > +#define CORE_COMMIT_CLEAR 0x3000 > +#define CORE_COMMIT_SHIFT 12 > +#define HISI_ETM_AMBA_ID_V1 0x000b6d01 > + > static int pm_save_enable = PARAM_PM_SAVE_FIRMWARE; > module_param(pm_save_enable, int, 0444); > MODULE_PARM_DESC(pm_save_enable, > @@ -104,11 +108,40 @@ struct etm4_enable_arg { > int rc; > }; > > +static void etm4_cpu_actlr1_cfg(void *info) > +{ > + struct etm4_enable_arg *arg = (struct etm4_enable_arg *)info; > + u64 val; > + > + asm volatile("mrs %0,s3_1_c15_c2_5" : "=r"(val)); > + val &= ~CORE_COMMIT_CLEAR; > + val |= arg->rc << CORE_COMMIT_SHIFT; > + asm volatile("msr s3_1_c15_c2_5,%0" : : "r"(val)); > +} > + > +static void etm4_config_core_commit(int cpu, int val) > +{ > + struct etm4_enable_arg arg = {0}; > + > + arg.rc = val; > + smp_call_function_single(cpu, etm4_cpu_actlr1_cfg, &arg, 1); Function etm4_enable/disable_hw() are already running on the CPU they are supposed to so no need to call smp_call_function_single(). > +} > + > static int etm4_enable_hw(struct etmv4_drvdata *drvdata) > { > int i, rc; > + struct amba_device *adev; > struct etmv4_config *config = &drvdata->config; > struct device *etm_dev = &drvdata->csdev->dev; > + struct device *dev = drvdata->csdev->dev.parent; > + > + adev = container_of(dev, struct amba_device, dev); > + /* > + * If ETM device is HiSilicon ETM device, reduce the > + * core-commit to avoid ETM overflow. > + */ > + if (adev->periphid == HISI_ETM_AMBA_ID_V1) Do you have any documentation on this back pressure feature? I doubt this is specific to Hip09 platform and as such would prefer to have a more generic approach that works on any platform that supports it. Anyone on the CS mailing list that knows what this is about? Thanks, Mathieu > + etm4_config_core_commit(drvdata->cpu, 1); > > CS_UNLOCK(drvdata->base); > > @@ -472,10 +505,20 @@ static void etm4_disable_hw(void *info) > { > u32 control; > struct etmv4_drvdata *drvdata = info; > + struct device *dev = drvdata->csdev->dev.parent; > struct etmv4_config *config = &drvdata->config; > struct device *etm_dev = &drvdata->csdev->dev; > + struct amba_device *adev; > int i; > > + adev = container_of(dev, struct amba_device, dev); > + /* > + * If ETM device is HiSilicon ETM device, resume the > + * core-commit after ETM trace is complete. > + */ > + if (adev->periphid == HISI_ETM_AMBA_ID_V1) > + etm4_config_core_commit(drvdata->cpu, 0); > + > CS_UNLOCK(drvdata->base); > > if (!drvdata->skip_power_up) { > -- > 2.8.1 >