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Mon, 04 Aug 2025 01:48:27 -0700 (PDT) Message-ID: Date: Mon, 4 Aug 2025 10:48:29 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 11/19] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline and amd-cppc driver To: "Penny, Zheng" Cc: "Huang, Ray" , Andrew Cooper , Anthony PERARD , "Orzel, Michal" , Julien Grall , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Stefano Stabellini , "xen-devel@lists.xenproject.org" References: <20250711035106.2540522-1-Penny.Zheng@amd.com> <20250711035106.2540522-12-Penny.Zheng@amd.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 04.08.2025 10:09, Penny, Zheng wrote: > [Public] > >> -----Original Message----- >> From: Jan Beulich >> Sent: Thursday, July 17, 2025 12:00 AM >> To: Penny, Zheng >> Cc: Huang, Ray ; Andrew Cooper >> ; Anthony PERARD ; >> Orzel, Michal ; Julien Grall ; Roger Pau >> Monné ; Stefano Stabellini ; xen- >> devel@lists.xenproject.org >> Subject: Re: [PATCH v6 11/19] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline >> and amd-cppc driver >> >> On 11.07.2025 05:50, Penny Zheng wrote: >>> --- a/xen/arch/x86/acpi/cpufreq/cpufreq.c >>> +++ b/xen/arch/x86/acpi/cpufreq/cpufreq.c >>> @@ -128,12 +128,14 @@ static int __init cf_check >>> cpufreq_driver_init(void) >>> >>> if ( cpufreq_controller == FREQCTL_xen ) >>> { >>> + unsigned int i = 0; >> >> Pointless initializer; both for() loops set i to 0. But also see further down. >> >>> @@ -157,9 +164,70 @@ static int __init cf_check >>> cpufreq_driver_init(void) >>> >>> case X86_VENDOR_AMD: >>> case X86_VENDOR_HYGON: >>> - ret = IS_ENABLED(CONFIG_AMD) ? powernow_register_driver() : - >> ENODEV; >>> + if ( !IS_ENABLED(CONFIG_AMD) ) >>> + { >>> + ret = -ENODEV; >>> + break; >>> + } >>> + ret = -ENOENT; >> >> The code structure is sufficiently different from the Intel counterpart for this to >> perhaps better move ... >> >>> + for ( i = 0; i < cpufreq_xen_cnt; i++ ) >>> + { >>> + switch ( cpufreq_xen_opts[i] ) >>> + { >>> + case CPUFREQ_xen: >>> + ret = powernow_register_driver(); >>> + break; >>> + >>> + case CPUFREQ_amd_cppc: >>> + ret = amd_cppc_register_driver(); >>> + break; >>> + >>> + case CPUFREQ_none: >>> + ret = 0; >>> + break; >>> + >>> + default: >>> + printk(XENLOG_WARNING >>> + "Unsupported cpufreq driver for vendor AMD or Hygon\n"); >>> + break; >> >> ... here. >> > > Are we suggesting moving > " > if ( !IS_ENABLED(CONFIG_AMD) ) > { > ret = -ENODEV; > break; > } > " here? In which case, When CONFIG_AMD=n and users doesn't provide "cpufreq=xxx", we will have cpufreq_xen_cnt initialized as 1 and cpufreq_xen_opts[0] = CPUFREQ_xen. powernow_register_driver() hence gets invoked. The thing is that we don't have stub for it and it is compiled under CONFIG_AMD > I suggest to change to use #ifdef CONFIG_AMD code wrapping > >>> + } >>> + >>> + if ( !ret || ret == -EBUSY ) >>> + break; >>> + } >>> + >>> break; >>> } >>> + >>> + /* >>> + * After successful cpufreq driver registeration, >> XEN_PROCESSOR_PM_CPPC >>> + * and XEN_PROCESSOR_PM_PX shall become exclusive flags. >>> + */ >>> + if ( !ret ) >>> + { >>> + ASSERT(i < cpufreq_xen_cnt); >>> + switch ( cpufreq_xen_opts[i] ) >> >> Hmm, this is using the the initializer of i that I commented on. I think there's >> another default: case missing, where you simply "return 0" (to retain prior behavior). >> But again see also yet further down. >> >> >>> + /* >>> + * No cpufreq driver gets registered, clear both >>> + * XEN_PROCESSOR_PM_CPPC and XEN_PROCESSOR_PM_PX >>> + */ >>> + xen_processor_pmbits &= ~(XEN_PROCESSOR_PM_CPPC | >>> + XEN_PROCESSOR_PM_PX); >> >> Yet more hmm - this path you want to get through for the case mentioned above. >> But only this code; specifically not the "switch ( cpufreq_xen_opts[i] )", which really >> is "switch ( cpufreq_xen_opts[0] )" in that case, and that's pretty clearly wrong to >> evaluate in then. > > Correct me if I understand you wrongly: > The above "case missing" , are we talking about is entering "case CPUFREQ_none" ? > IMO, it may never be entered. If users doesn't provide "cpufreq=xxx", we will have cpufreq_xen_cnt initialized as 1 and cpufreq_xen_opts[0] = CPUFREQ_xen. That is, we will have px states as default driver. Even if we have failed px-driver initialization, with cpufreq_xen_cnt limited to 1, we will not enter CPUFREQ_none. > CPUFREQ_none only could be set when users explicitly set "cpufreq=disabled/none/0", but in which case, cpufreq_controller will be set with FREQCTL_none. And the whole cpufreq_driver_init() is under " cpufreq_controller == FREQCTL_xen " condition > Or "case missing" is referring entering default case? In which case, we will have -ENOENT errno. As we have ret=-ENOENT in the very beginning Sorry, this is hard to follow. Plus I think I made the main requirement quite clear: You want to "retain prior behavior" for all cases you don't deliberately change to accommodate the new driver. Plus you want to watch out for pre- existing incorrect behavior: Rather than proliferating any, such would want adjusting. Jan