Re: [PATCH v2 08/13] ACPICA: Hardware: Add optimized access bit width support

Boris Ostrovsky
2016-05-25T19:17:26Z

On 05/05/2016 12:58 AM, Lv Zheng wrote:
> ACPICA commit c49a751b4dae7baec1790748a2b4b6e8ab599f51
>
> For Access Size = 0, it actually can use user expected access bit width.
> This patch implements this.
>
> Besides of the ACPICA upstream commit, this patch also includes a fix fixing
> the issue reported by the FreeBSD community.
> The old register descriptors are translated in acpi_tb_init_generic_address()
> with access_width being filled with 0. This breaks code in
> acpi_hw_get_access_bit_width() when the registers are 16-bit IO ports and their
> bit_width fields are filled with 16. The rapid fix is meant to make code
> written for acpi_hw_get_access_bit_width() regression safer before the issue is
> correctly fixed from acpi_tb_init_generic_address(). Reported by
> John Baldwin <jhb@freebsd.org>, fixed by Lv Zheng <lv.zheng@intel.com>, tested
> by Jung-uk Kim <jkim@freebsd.org>.
>
> Link: https://github.com/acpica/acpica/commit/c49a751b
> Reported-by: John Baldwin <jhb@freebsd.org>
> Tested-by Jung-uk Kim <jkim@freebsd.org>.
> Signed-off-by: Lv Zheng <lv.zheng@intel.com>
> Signed-off-by: Bob Moore <robert.moore@intel.com>
> ---
> drivers/acpi/acpica/hwregs.c | 49 ++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 47 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/acpica/hwregs.c b/drivers/acpi/acpica/hwregs.c
> index 035fb52..892e677 100644
> --- a/drivers/acpi/acpica/hwregs.c
> +++ b/drivers/acpi/acpica/hwregs.c
> @@ -51,6 +51,10 @@ ACPI_MODULE_NAME("hwregs")
>
> #if (!ACPI_REDUCED_HARDWARE)
> /* Local Prototypes */
> +static u8
> +acpi_hw_get_access_bit_width(struct acpi_generic_address *reg,
> + u8 max_bit_width);
> +
> static acpi_status
> acpi_hw_read_multiple(u32 *value,
> struct acpi_generic_address *register_a,
> @@ -65,6 +69,48 @@ acpi_hw_write_multiple(u32 value,
>
> /******************************************************************************
> *
> + * FUNCTION: acpi_hw_get_access_bit_width
> + *
> + * PARAMETERS: reg - GAS register structure
> + * max_bit_width - Max bit_width supported (32 or 64)
> + *
> + * RETURN: Status
> + *
> + * DESCRIPTION: Obtain optimal access bit width
> + *
> + ******************************************************************************/
> +
> +static u8
> +acpi_hw_get_access_bit_width(struct acpi_generic_address *reg, u8 max_bit_width)
> +{
> + u64 address;
> +
> + if (!reg->access_width) {
> + /*
> + * Detect old register descriptors where only the bit_width field
> + * makes senses. The target address is copied to handle possible
> + * alignment issues.
> + */
> + ACPI_MOVE_64_TO_64(&address, &reg->address);
> + if (!reg->bit_offset && reg->bit_width &&
> + ACPI_IS_POWER_OF_TWO(reg->bit_width) &&
> + ACPI_IS_ALIGNED(reg->bit_width, 8) &&
> + ACPI_IS_ALIGNED(address, reg->bit_width)) {
> + return (reg->bit_width);
> + } else {
> + if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
> + return (32);

This (together with "... Add access_width/bit_offset support in
acpi_hw_write") breaks Xen guests using older QEMU which doesn't support
4-byte IO accesses.

Why not return "reg->bit_width?:max_bit_width" ? This will preserve
original behavior.

-boris

> + } else {
> + return (max_bit_width);
> + }
> + }
> + } else {
> + return (1 << (reg->access_width + 2));
> + }
> +}
> +
> +/******************************************************************************
> + *
> * FUNCTION: acpi_hw_validate_register
> *
> * PARAMETERS: reg - GAS register structure
> @@ -122,8 +168,7 @@ acpi_hw_validate_register(struct acpi_generic_address *reg,
>
> /* Validate the bit_width, convert access_width into number of bits */
>
> - access_width = reg->access_width ? reg->access_width : 1;
> - access_width = 1 << (access_width + 2);
> + access_width = acpi_hw_get_access_bit_width(reg, max_bit_width);
> bit_width =
> ACPI_ROUND_UP(reg->bit_offset + reg->bit_width, access_width);
> if (max_bit_width < bit_width) {