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b=sd0fXd0N0pG4d/wwRy1ilpuKLhz8TPpV8EvfDl7JZxDW/qGU3Pr5gIcL++xHSmbIvkbGjXzgx0Ll3jVUsul6dsFEnKpRzhyyTGE/YUhFBRt/rTNIbfu08x18vuBHYCpb+GumFVMQs1XVNwWvH+yRZEZMDq03DVVO+XNwRvOgYog= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from PH8PR12MB6914.namprd12.prod.outlook.com (2603:10b6:510:1cb::21) by LVUPR12MB999159.namprd12.prod.outlook.com (2603:10b6:408:3a4::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9891.15; Wed, 3 Jun 2026 18:53:23 +0000 Received: from PH8PR12MB6914.namprd12.prod.outlook.com ([fe80::2893:177a:72b0:6000]) by PH8PR12MB6914.namprd12.prod.outlook.com ([fe80::2893:177a:72b0:6000%6]) with mapi id 15.21.0092.006; Wed, 3 Jun 2026 18:53:23 +0000 Message-ID: <2e3a5f9a-69fe-4790-8b8b-2d1622977a2f@amd.com> Date: Wed, 3 Jun 2026 13:53:18 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] cpufreq/amd-pstate: Fix EPP initialization for shared memory systems Content-Language: en-US To: Marco Scardovi , kprateek.nayak@amd.com Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, perry.yuan@amd.com, rafael@kernel.org, ray.huang@amd.com, stuartmeckle@gmail.com, viresh.kumar@linaro.org, wyes.karny@amd.com References: <4cb9459c-f471-478a-9670-58d898619f45@amd.com> <20260603120121.25772-1-scardracs@disroot.org> <20260603120121.25772-2-scardracs@disroot.org> From: Mario Limonciello In-Reply-To: <20260603120121.25772-2-scardracs@disroot.org> Content-Type: text/plain; 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Because the > requested EPP (0) matches the uninitialized cached value (0), the early > return check (epp == epp_cached) triggers, and the driver skips writing > to the hardware. > > The cppc_set_epp_perf() helper is responsible for writing both the EPP > register and the CPPC autonomous mode enable register (auto_sel). Skipping > the EPP write on initialization due to the false cache hit consequently > skips setting auto_sel to 1, leaving the CPU in non-autonomous mode. This > prevents the hardware from boosting and leaves the CPU frequency stuck at > the lowest non-linear frequency (1.7GHz). > > Fix this by introducing an `epp_hw_programmed` flag in struct amd_cpudata > to track whether EPP has been configured on the hardware. Bypass the early > return check in shmem_set_epp() if EPP has not yet been programmed on the > hardware. Once EPP has been successfully programmed once, the cached EPP > value becomes authoritative (representing driver intent rather than dynamic > firmware state), allowing subsequent runtime mode transitions to use the > cache guard optimization safely. > > Fixes: ffa5096a7c33 ("cpufreq: amd-pstate: implement Pstate EPP support for the AMD processors") > Link: https://bugzilla.kernel.org/show_bug.cgi?id=221473 > Assisted-by: Antigravity:gemini-3.5-flash > Signed-off-by: Marco Scardovi > --- > drivers/cpufreq/amd-pstate.c | 9 ++++++++- > drivers/cpufreq/amd-pstate.h | 2 ++ > 2 files changed, 10 insertions(+), 1 deletion(-) > > diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c > index 8d55e2be825b..e8057f3dfb1e 100644 > --- a/drivers/cpufreq/amd-pstate.c > +++ b/drivers/cpufreq/amd-pstate.c > @@ -424,7 +424,13 @@ static int shmem_set_epp(struct cpufreq_policy *policy, u8 epp) > epp != epp_cached); > } > > - if (epp == epp_cached) > + /* > + * After the first successful programming, the cached EPP value > + * becomes authoritative (representing driver intent rather than > + * dynamic firmware state), allowing us to skip redundant hardware > + * writes when the EPP value is unchanged. > + */ > + if (cpudata->epp_hw_programmed && epp == epp_cached) > return 0; > > perf_ctrls.energy_perf = epp; > @@ -434,6 +440,7 @@ static int shmem_set_epp(struct cpufreq_policy *policy, u8 epp) > return ret; > } > > + cpudata->epp_hw_programmed = true; > value = READ_ONCE(cpudata->cppc_req_cached); > FIELD_MODIFY(AMD_CPPC_EPP_PERF_MASK, &value, epp); > WRITE_ONCE(cpudata->cppc_req_cached, value); > diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h > index e4722e54387b..fc6cd4b873f6 100644 > --- a/drivers/cpufreq/amd-pstate.h > +++ b/drivers/cpufreq/amd-pstate.h > @@ -128,6 +128,8 @@ struct amd_cpudata { > u8 epp_default_dc; > bool dynamic_epp; > bool raw_epp; > + /* Indicates that EPP has been successfully programmed at least once since boot. */ > + bool epp_hw_programmed; > struct notifier_block power_nb; > > /* platform profile */ I'm having a hard time following why this is needed. Let me explain my chain of thought. We start at amd_pstate_epp_cpu_init(). * cpudata (and thus cppc_req_cached) is initalized to 0 via kzalloc() - On a server we initialize "epp_default" via a lookup to the HW (amd_pstate_get_epp). - On a non-server we initialize "epp_default" to 0x80. * we call amd_pstate_set_epp() with epp_deafult as the argument. Now in the shared mem backend (shmem_set_epp) we do a lookup of epp_cached and it should be 0. We do a comparison of the argument sent to the function, and this should be 0x80. So how do we get into a case that amd_pstate_set_epp() is actually called with 0? There are some trace points specifically for this purpose - you could confirm there really is such a call by using them at bootup (or by starting in passive and with a mode change to active at runtime). Then we call amd_pstate_set_epp() with that epp_default value.