linux-kernel - Re: [PATCH v6 1/6] acpi: cppc: Add min and max perf reg writing support

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Message-ID: <Y+zZQV+63uGnQbUA@amd.com>
Date:   Wed, 15 Feb 2023 21:08:17 +0800
From:   Huang Rui <ray.huang@....com>
To:     "Karny, Wyes" <Wyes.Karny@....com>
Cc:     Rafael J Wysocki <rafael@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        "Yuan, Perry" <Perry.Yuan@....com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        "Shukla, Santosh" <Santosh.Shukla@....com>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        "Narayan, Ananth" <Ananth.Narayan@....com>,
        "Shenoy, Gautham Ranjal" <gautham.shenoy@....com>,
        Tor Vic <torvic9@...lbox.org>
Subject: Re: [PATCH v6 1/6] acpi: cppc: Add min and max perf reg writing
 support

On Tue, Feb 07, 2023 at 01:21:52AM +0800, Karny, Wyes wrote:
> Currently writing of min and max perf register is deferred in
> cppc_set_perf function. In CPPC guided mode, these registers needed to
> be written to guide the platform about min and max perf levels. Add this support
> to make guided mode work properly on AMD shared memory systems.
> 
> Signed-off-by: Wyes Karny <wyes.karny@....com>
> Reviewed-by: Mario Limonciello <mario.limonciello@....com>

Acked-by: Huang Rui <ray.huang@....com>

> ---
>  drivers/acpi/cppc_acpi.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 02d83c807271..91f9ef75f7de 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1487,7 +1487,7 @@ EXPORT_SYMBOL_GPL(cppc_set_enable);
>  int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>  {
>  	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> -	struct cpc_register_resource *desired_reg;
> +	struct cpc_register_resource *desired_reg, *min_perf_reg, *max_perf_reg;
>  	int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
>  	struct cppc_pcc_data *pcc_ss_data = NULL;
>  	int ret = 0;
> @@ -1498,6 +1498,8 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>  	}
>  
>  	desired_reg = &cpc_desc->cpc_regs[DESIRED_PERF];
> +	min_perf_reg = &cpc_desc->cpc_regs[MIN_PERF];
> +	max_perf_reg = &cpc_desc->cpc_regs[MAX_PERF];
>  
>  	/*
>  	 * This is Phase-I where we want to write to CPC registers
> @@ -1506,7 +1508,7 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>  	 * Since read_lock can be acquired by multiple CPUs simultaneously we
>  	 * achieve that goal here
>  	 */
> -	if (CPC_IN_PCC(desired_reg)) {
> +	if (CPC_IN_PCC(desired_reg) || CPC_IN_PCC(min_perf_reg) || CPC_IN_PCC(max_perf_reg)) {
>  		if (pcc_ss_id < 0) {
>  			pr_debug("Invalid pcc_ss_id\n");
>  			return -ENODEV;
> @@ -1529,13 +1531,19 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>  		cpc_desc->write_cmd_status = 0;
>  	}
>  
> -	/*
> -	 * Skip writing MIN/MAX until Linux knows how to come up with
> -	 * useful values.
> -	 */
>  	cpc_write(cpu, desired_reg, perf_ctrls->desired_perf);
>  
> -	if (CPC_IN_PCC(desired_reg))
> +	/**
> +	 * Only write if min_perf and max_perf not zero. Some drivers pass zero
> +	 * value to min and max perf, but they don't mean to set the zero value,
> +	 * they just don't want to write to those registers.
> +	 */
> +	if (perf_ctrls->min_perf)
> +		cpc_write(cpu, min_perf_reg, perf_ctrls->min_perf);
> +	if (perf_ctrls->max_perf)
> +		cpc_write(cpu, max_perf_reg, perf_ctrls->max_perf);
> +
> +	if (CPC_IN_PCC(desired_reg) || CPC_IN_PCC(min_perf_reg) || CPC_IN_PCC(max_perf_reg))
>  		up_read(&pcc_ss_data->pcc_lock);	/* END Phase-I */
>  	/*
>  	 * This is Phase-II where we transfer the ownership of PCC to Platform
> @@ -1583,7 +1591,7 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>  	 * case during a CMD_READ and if there are pending writes it delivers
>  	 * the write command before servicing the read command
>  	 */
> -	if (CPC_IN_PCC(desired_reg)) {
> +	if (CPC_IN_PCC(desired_reg) || CPC_IN_PCC(min_perf_reg) || CPC_IN_PCC(max_perf_reg)) {
>  		if (down_write_trylock(&pcc_ss_data->pcc_lock)) {/* BEGIN Phase-II */
>  			/* Update only if there are pending write commands */
>  			if (pcc_ss_data->pending_pcc_write_cmd)
> -- 
> 2.34.1
>