Re: [PATCH v1 1/1] ACPI: CPPC: Fix access width used for PCC registers

Easwar Hariharan
2024-04-01T16:48:28Z

Hi Vanshi,

Thanks for testing and catching this. One comment below, but Jarred is OOF for a couple days so
we'll get back again after testing on our platform.

On 3/29/2024 3:00 PM, Vanshidhar Konda wrote:
> Commit 2f4a4d63a193 ("ACPI: CPPC: Use access_width over bit_width for
> system memory accesses") 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.
>
> Fixes: 2f4a4d63a193 ("ACPI: CPPC: Use access_width over bit_width for system memory accesses")
> Signed-off-by: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
> ---
>
> 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.
>
> drivers/acpi/cppc_acpi.c | 45 +++++++++++++++++++++++++++++-----------
> 1 file changed, 33 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 4bfbe55553f4..23d16a1ee878 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);
> @@ -1018,8 +1018,15 @@ 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)
> @@ -1028,8 +1035,6 @@ static int cpc_read(int cpu, struct cpc_register_resource *reg_res, u64 *val)
> return acpi_os_read_memory((acpi_physical_address)reg->address,
> val, reg->bit_width);
>
> - size = GET_BIT_WIDTH(reg);
> -
> switch (size) {
> case 8:
> *val = readb_relaxed(vaddr);
> @@ -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",
> + if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
> + pr_debug("Error: Cannot read %u width from for system memory: 0x%llx\n",
> + reg->bit_width, reg->address);
> + } else if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
> + pr_debug("Error: Cannot read %u bit width to PCC for ss: %d\n",
> reg->bit_width, 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);
> @@ -1076,8 +1087,15 @@ 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)
> @@ -1086,8 +1104,6 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
> return acpi_os_write_memory((acpi_physical_address)reg->address,
> val, reg->bit_width);
>
> - size = GET_BIT_WIDTH(reg);
> -
> 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",
> + if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
> + pr_debug("Error: Cannot write %u width from for system memory: 0x%llx\n",
> + reg->bit_width, reg->address);
^^^^^^^^^^^^^^
Shouldn't this be size = GET_BIT_WIDTH(reg) instead of reg->bit_width? I think this is falling back to the
previous behavior where it assumes access_width was not provided by the platform firmware.

> + } else if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
> + pr_debug("Error: Cannot write %u bit width to PCC for ss: %d\n",
> reg->bit_width, pcc_ss_id);
> + }
> ret_val = -EFAULT;
> break;
> }

Thanks,
Easwar