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h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ICKRfZ//3qfKeVZr21+0SuAGPaSpbRnfIDT1zrsikAhtxFsbEpT9NLH3T/Nl0RO3K lHOLA19TPZ9gJy5fGPLbTudj5vqbniwiRmnCM4GC3vGyvF05OAerBgPbSolxqPE9WI ORnnblsYb/gfmcSPlRC3tHzS1RWU6jqDXvxpnrDw= Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.codeaurora.org (Postfix) with ESMTP id 44BD4608FC; Thu, 21 Mar 2019 20:02:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1553198547; bh=xenGAl2NHl8X7iP879+uW3awyNqe6NGTDdJhQWw9rkE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=LNuzlWzv6u/F4HqZjjFZ/ZDnQwSnnXGLfkI1DAlLA1v+vvDo1qRu6J6ZWkRMYP0DT ecojn3keh6ieLpi7uVtDc/DYUgP/ZcjLZkSVKvxANBPIyccbNM842qzUOEaS+igfOI P4pF3k8oEy9UrSWZoaasK4vCu8AOoDoR/OBsfYoM= MIME-Version: 1.0 Date: Thu, 21 Mar 2019 13:02:27 -0700 From: Sodagudi Prasad To: Julien Thierry Subject: Re: [PATCH] perf: Change PMCR write to read-modify-write In-Reply-To: References: <1553134066-20272-1-git-send-email-psodagud@codeaurora.org> Message-ID: X-Sender: psodagud@codeaurora.org User-Agent: Roundcube Webmail/1.2.5 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190321_130229_627435_066032F3 X-CRM114-Status: GOOD ( 17.19 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peterz@infradead.org, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, mingo@redhat.com, linux-arm-kernel@lists.infradead.org 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 2019-03-21 06:34, Julien Thierry wrote: > Hi Prasad, > > On 21/03/2019 02:07, Prasad Sodagudi wrote: >> Preserves the bitfields of PMCR_EL0(AArch64) during PMU reset. >> Reset routine should write a 1 to PMCR.C and PMCR.P fields only >> to reset the counters. Other fields should not be changed >> as they could be set before PMU initialization and their >> value must be preserved even after reset. >> > > Are there any particular bit you are concerned about? Apart from the RO > ones and the Res0 ones (to which we are already writing 0), I see: > > DP -> irrelevant for non-secure > X -> This one is the only potentially interesting, however it resets to > an architecturally unknown value, so unless we know for a fact it was > set before hand, we probably want to clear it > D -> ignored when we have LC set (and we do) > E -> Since this is the function we use to reset the PMU on the current > CPU, we probably want to set this bit to 0 regardless of its previous > value > > So, is there any issue this patch is solving? Hi Julien, Thanks for taking a look into this patch. Yes. On our Qualcomm platforms, observed that X bit is getting cleared by kernel. This bit is getting set by firmware for Qualcomm use cases and non-secure world is resetting without this patch. I think, changing that register this register modifications to read-modify-write style make sense. -Thanks, Prasad > > Thanks, > >> Signed-off-by: Prasad Sodagudi >> --- >> arch/arm64/kernel/perf_event.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/kernel/perf_event.c >> b/arch/arm64/kernel/perf_event.c >> index 4addb38..0c1afdd 100644 >> --- a/arch/arm64/kernel/perf_event.c >> +++ b/arch/arm64/kernel/perf_event.c >> @@ -868,8 +868,8 @@ static void armv8pmu_reset(void *info) >> * Initialize & Reset PMNC. Request overflow interrupt for >> * 64 bit cycle counter but cheat in armv8pmu_write_counter(). >> */ >> - armv8pmu_pmcr_write(ARMV8_PMU_PMCR_P | ARMV8_PMU_PMCR_C | >> - ARMV8_PMU_PMCR_LC); >> + armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_P | >> + ARMV8_PMU_PMCR_C | ARMV8_PMU_PMCR_LC); >> } >> >> static int __armv8_pmuv3_map_event(struct perf_event *event, >> -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, Linux Foundation Collaborative Project _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel