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Message-ID: <5f3f0bbf-8d17-47b0-bbc2-1bdcc1e1a733@linux.microsoft.com>
Date: Thu, 11 Apr 2024 15:07:55 -0700
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Subject: Re: [PATCH v2] ACPI: CPPC: Fix access width used for PCC registers
To: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>,
 Jarred White <jarredwhite@linux.microsoft.com>
Cc: "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
 linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
 "5 . 15+" <stable@vger.kernel.org>
References: <20240411212306.1359466-1-vanshikonda@os.amperecomputing.com>
Content-Language: en-CA
From: Easwar Hariharan <eahariha@linux.microsoft.com>
In-Reply-To: <20240411212306.1359466-1-vanshikonda@os.amperecomputing.com>
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On 4/11/2024 2:23 PM, Vanshidhar Konda wrote:
> commit 2f4a4d63a193be6fd530d180bb13c3592052904c modified
> cpc_read/cpc_write to use access_width to read CPC registers. For PCC
> registers the access width field in the ACPI register macro specifies
> the PCC subspace id. For non-zero PCC subspace id the access width is
> incorrectly treated as access width. This causes errors when reading
> from PCC registers in the CPPC driver.
> 
> For PCC registers base the size of read/write on the bit width field.
> The debug message in cpc_read/cpc_write is updated to print relevant
> information for the address space type used to read the register.
> 
> Signed-off-by: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
> Tested-by: Jarred White <jarredwhite@linux.microsoft.com>
> Reviewed-by: Jarred White <jarredwhite@linux.microsoft.com>
> Cc: 5.15+ <stable@vger.kernel.org> # 5.15+
> ---
> 
> When testing v6.9-rc1 kernel on AmpereOne system dmesg showed that
> cpufreq policy had failed to initialize on some cores during boot because
> cpufreq->get() always returned 0. On this system CPPC registers are in PCC
> subspace index 2 that are 32 bits wide. With this patch the CPPC driver
> interpreted the access width field as 16 bits, causing the register read
> to roll over too quickly to provide valid values during frequency
> computation.
> 
> v2:
> - Use size variable in debug print message
> - Use size instead of reg->bit_width for acpi_os_read_memory and
>   acpi_os_write_memory
> 
>  drivers/acpi/cppc_acpi.c | 53 ++++++++++++++++++++++++++++------------
>  1 file changed, 37 insertions(+), 16 deletions(-)

Thanks for adding the CC: stable tag. Couple of nits, assuming those are fixed:

Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>

> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 4bfbe55553f4..a037e9d15f48 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1002,14 +1002,14 @@ static int cpc_read(int cpu, struct cpc_register_resource *reg_res, u64 *val)
>  	}
>  
>  	*val = 0;
> +	size = GET_BIT_WIDTH(reg);
>  
>  	if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
> -		u32 width = GET_BIT_WIDTH(reg);
>  		u32 val_u32;
>  		acpi_status status;
>  
>  		status = acpi_os_read_port((acpi_io_address)reg->address,
> -					   &val_u32, width);
> +					   &val_u32, size);
>  		if (ACPI_FAILURE(status)) {
>  			pr_debug("Error: Failed to read SystemIO port %llx\n",
>  				 reg->address);
> @@ -1018,17 +1018,22 @@ static int cpc_read(int cpu, struct cpc_register_resource *reg_res, u64 *val)
>  
>  		*val = val_u32;
>  		return 0;
> -	} else if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM && pcc_ss_id >= 0)
> +	} else if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM && pcc_ss_id >= 0) {
> +		/*
> +		 * For registers in PCC space, the register size is determined
> +		 * by the bit width field; the access size is used to indicate
> +		 * the PCC subspace id.
> +		 */
> +		size = reg->bit_width;
>  		vaddr = GET_PCC_VADDR(reg->address, pcc_ss_id);
> +	}
>  	else if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
>  		vaddr = reg_res->sys_mem_vaddr;
>  	else if (reg->space_id == ACPI_ADR_SPACE_FIXED_HARDWARE)
>  		return cpc_read_ffh(cpu, reg, val);
>  	else
>  		return acpi_os_read_memory((acpi_physical_address)reg->address,
> -				val, reg->bit_width);
> -
> -	size = GET_BIT_WIDTH(reg);
> +				val, size);
>  
>  	switch (size) {
>  	case 8:
> @@ -1044,8 +1049,13 @@ static int cpc_read(int cpu, struct cpc_register_resource *reg_res, u64 *val)
>  		*val = readq_relaxed(vaddr);
>  		break;
>  	default:
> -		pr_debug("Error: Cannot read %u bit width from PCC for ss: %d\n",
> -			 reg->bit_width, pcc_ss_id);
> +		if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
> +			pr_debug("Error: Cannot read %u width from for system memory: 0x%llx\n",
> +				size, reg->address);

Nit: from for? There might be a missing word there, or just an extra. Ditto for cpc_write() below.

> +		} else if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
> +			pr_debug("Error: Cannot read %u bit width to PCC for ss: %d\n",
> +				size, pcc_ss_id);
> +		}
>  		return -EFAULT;
>  	}
>  
> @@ -1063,12 +1073,13 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
>  	int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
>  	struct cpc_reg *reg = &reg_res->cpc_entry.reg;
>  
> +	size = GET_BIT_WIDTH(reg);
> +
>  	if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
> -		u32 width = GET_BIT_WIDTH(reg);
>  		acpi_status status;
>  
>  		status = acpi_os_write_port((acpi_io_address)reg->address,
> -					    (u32)val, width);
> +					    (u32)val, size);
>  		if (ACPI_FAILURE(status)) {
>  			pr_debug("Error: Failed to write SystemIO port %llx\n",
>  				 reg->address);
> @@ -1076,17 +1087,22 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
>  		}
>  
>  		return 0;
> -	} else if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM && pcc_ss_id >= 0)
> +	} else if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM && pcc_ss_id >= 0) {
> +		/*
> +		 * For registers in PCC space, the register size is determined
> +		 * by the bit width field; the access size is used to indicate
> +		 * the PCC subspace id.
> +		 */
> +		size = reg->bit_width;
>  		vaddr = GET_PCC_VADDR(reg->address, pcc_ss_id);
> +	}
>  	else if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
>  		vaddr = reg_res->sys_mem_vaddr;
>  	else if (reg->space_id == ACPI_ADR_SPACE_FIXED_HARDWARE)
>  		return cpc_write_ffh(cpu, reg, val);
>  	else
>  		return acpi_os_write_memory((acpi_physical_address)reg->address,
> -				val, reg->bit_width);
> -
> -	size = GET_BIT_WIDTH(reg);
> +				val, size);
>  
>  	if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
>  		val = MASK_VAL(reg, val);
> @@ -1105,8 +1121,13 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
>  		writeq_relaxed(val, vaddr);
>  		break;
>  	default:
> -		pr_debug("Error: Cannot write %u bit width to PCC for ss: %d\n",
> -			 reg->bit_width, pcc_ss_id);
> +		if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
> +			pr_debug("Error: Cannot write %u width from for system memory: 0x%llx\n",
> +				size, reg->address);
> +		} else if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
> +			pr_debug("Error: Cannot write %u bit width to PCC for ss: %d\n",
> +				size, pcc_ss_id);
> +		}
>  		ret_val = -EFAULT;
>  		break;
>  	}