Re: [RESEND PATCH v2] acpi: Use access_width over register_width for system memory accesses

Rafael J. Wysocki
2023-12-21T14:13:01Z

On Sat, Dec 16, 2023 at 1:13 AM Jarred White
<jarredwhite@linux.microsoft.com> wrote:
>
> To align with ACPI 6.3+, since bit_width can be any 8-bit value, we cannot
> depend on it being always on a clean 8b boundary.

So presumably, there are systems out there in which the platform
firmware uses bit_width that is not on a clean 8-bit boundary.

It would be good to mention them here.

> Instead, use access_width
> to determine the size and use the offset and width to shift and mask the
> bits we want to read/write out. Make sure to add a check for system memory
> since pcc redefines the access_width to subspace id.

And it would be good to add a comment to the code for it too.

>
> Signed-off-by: Jarred White <jarredwhite@linux.microsoft.com>
> ---
> Original thread
> https://lore.kernel.org/all/20230925180552.76071-1-jarredwhite@linux.microsoft.com/
> ---
> changelog:
> v1-->v2:
> 1. Fixed coding style errors
> 2. Backwards compatibility with ioremapping of address still an
> open question. Suggestions are welcomed.
>
> drivers/acpi/cppc_acpi.c | 36 +++++++++++++++++++++++++++++++-----
> 1 file changed, 31 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 7ff269a78c20..fb37e1727bf8 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -163,6 +163,13 @@ show_cppc_data(cppc_get_perf_caps, cppc_perf_caps, nominal_freq);
> show_cppc_data(cppc_get_perf_ctrs, cppc_perf_fb_ctrs, reference_perf);
> show_cppc_data(cppc_get_perf_ctrs, cppc_perf_fb_ctrs, wraparound_time);
>
> +/* Use access_width to determine the total number of bits */
> +#define ACCESS_WIDTH_TO_BITS(reg) 8 << ((reg)->access_width - 1)

Consider adding parens around the entire expression, or you may get
unexpected results.

> +
> +/* Shift and apply the mask for CPC reads/writes */
> +#define MASK_VAL(val) (((val) >> reg->bit_offset) & \
> + GENMASK((reg->bit_width), 0))

'reg' should be an argument of the macro or it will be prone to subtle mistakes.

> +
> static ssize_t show_feedback_ctrs(struct kobject *kobj,
> struct kobj_attribute *attr, char *buf)
> {
> @@ -777,6 +784,7 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
> } else if (gas_t->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
> if (gas_t->address) {
> void __iomem *addr;
> + size_t access_width;
>
> if (!osc_cpc_flexible_adr_space_confirmed) {
> pr_debug("Flexible address space capability not supported\n");
> @@ -784,7 +792,8 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
> goto out_free;
> }
>
> - addr = ioremap(gas_t->address, gas_t->bit_width/8);
> + access_width = ACCESS_WIDTH_TO_BITS(gas_t) / 8;

What would happen if the platform firmware incorrectly provided
reg->access_witdh == 0?

> + addr = ioremap(gas_t->address, access_width);
> if (!addr)
> goto out_free;
> cpc_ptr->cpc_regs[i-2].sys_mem_vaddr = addr;
> @@ -980,6 +989,7 @@ int __weak cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val)
> static int cpc_read(int cpu, struct cpc_register_resource *reg_res, u64 *val)
> {
> void __iomem *vaddr = NULL;
> + int size;
> int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
> struct cpc_reg *reg = &reg_res->cpc_entry.reg;
>
> @@ -991,7 +1001,7 @@ static int cpc_read(int cpu, struct cpc_register_resource *reg_res, u64 *val)
> *val = 0;
>
> if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
> - u32 width = 8 << (reg->access_width - 1);
> + u32 width = ACCESS_WIDTH_TO_BITS(reg);
> u32 val_u32;
> acpi_status status;
>
> @@ -1015,7 +1025,12 @@ 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);
>
> - switch (reg->bit_width) {
> + if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
> + size = ACCESS_WIDTH_TO_BITS(reg);
> + else
> + size = reg->bit_width;
> +
> + switch (size) {
> case 8:
> *val = readb_relaxed(vaddr);
> break;
> @@ -1034,18 +1049,22 @@ static int cpc_read(int cpu, struct cpc_register_resource *reg_res, u64 *val)
> return -EFAULT;
> }
>
> + if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
> + *val = MASK_VAL(*val);
> +
> return 0;
> }
>
> static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
> {
> int ret_val = 0;
> + int size;
> void __iomem *vaddr = NULL;
> int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
> struct cpc_reg *reg = &reg_res->cpc_entry.reg;
>
> if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
> - u32 width = 8 << (reg->access_width - 1);
> + u32 width = ACCESS_WIDTH_TO_BITS(reg);
> acpi_status status;
>
> status = acpi_os_write_port((acpi_io_address)reg->address,
> @@ -1067,7 +1086,14 @@ 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);
>
> - switch (reg->bit_width) {
> + if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
> + size = ACCESS_WIDTH_TO_BITS(reg);
> + val = MASK_VAL(val);
> + } else {
> + size = reg->bit_width;
> + }
> +
> + switch (size) {
> case 8:
> writeb_relaxed(val, vaddr);
> break;
> --