Re: [PATCH v1] ACPI/IORT: Workaround for IORT ID count "minus one" issue

Robin Murphy
2020-01-06T17:19:37Z

On 30/12/2019 12:27 pm, Hanjun Guo wrote:
> The IORT spec [0] says Number of IDs = The number of IDs in the range minus
> one, it is confusing but it was written down in the first version of the
> IORT spec. But the IORT ID mapping function iort_id_map() did something
> wrong from the start, which bails out if:
>
> the request ID >= the input base + number of IDs
>
> This is wrong because it ignored the "minus one", and breaks some valid
> usecases such as ID mapping to contain single device mapping without
> single mapping flag set.
>
> Pankaj Bansal proposed a solution to fix the issue [1], which bails
> out if:
>
> the request ID > the input base + number of IDs
>
> This works as the spec defined, unfortunately some firmware didn't
> minus one for the number of IDs in the range, and the propoased
> solution will break those systems in this way:
>
> PCI hostbridge mapping entry 1:
> Input base: 0x1000
> ID Count: 0x100
> Output base: 0x1000
> Output reference: 0xC4 //ITS reference
>
> PCI hostbridge mapping entry 2:
> Input base: 0x1100
> ID Count: 0x100
> Output base: 0x2000
> Output reference: 0xD4 //ITS reference
>
> Two mapping entries which the second entry's Input base = the first
> entry's Input base + ID count, so for requester ID 0x1100 will map
> to ITS 0xC4 not 0xD4 if we update '>=' to '>'.
>
> So introduce a workaround to match the IORT's OEM information for
> the broken firmware, also update the logic of the ID mapping for
> firmwares report the number of IDs as the IORT spec defined, to
> make the code compatible for both kinds of system.
>
> I checked the ACPI tables in the tianocore/edk2-platforms [2], only
> HiSilicon HIP07/08 did wrong, so just add HIP07/08 to the workaround
> info table, if we break other platforms, we can add that later.
>
> [0]: http://infocenter.arm.com/help/topic/com.arm.doc.den0049d/DEN0049D_IO_Remapping_Table.pdf
> [1]: https://patchwork.kernel.org/patch/11292823/
> [2]: https://github.com/tianocore/edk2-platforms
>
> Cc: Pankaj Bansal <pankaj.bansal@nxp.com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
> ---
>
> RFC->v1:
> - Print warning when matched the workaround info, suggested by Pankaj.
>
> drivers/acpi/arm64/iort.c | 55 ++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 52 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> index 33f7198..60eb10d 100644
> --- a/drivers/acpi/arm64/iort.c
> +++ b/drivers/acpi/arm64/iort.c
> @@ -298,6 +298,42 @@ static acpi_status iort_match_node_callback(struct acpi_iort_node *node,
> return status;
> }
>
> +struct iort_workaround_oem_info {
> + char oem_id[ACPI_OEM_ID_SIZE + 1];
> + char oem_table_id[ACPI_OEM_TABLE_ID_SIZE + 1];
> + u32 oem_revision;
> +};
> +
> +static bool apply_id_count_workaround;
> +
> +static struct iort_workaround_oem_info wa_info[] __initdata = {
> + {
> + .oem_id = "HISI ",
> + .oem_table_id = "HIP07 ",
> + .oem_revision = 0,
> + }, {
> + .oem_id = "HISI ",
> + .oem_table_id = "HIP08 ",
> + .oem_revision = 0,
> + }
> +};
> +
> +static void __init
> +iort_check_id_count_workaround(struct acpi_table_header *tbl)
> +{
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(wa_info); i++) {
> + if (!memcmp(wa_info[i].oem_id, tbl->oem_id, ACPI_OEM_ID_SIZE) &&
> + !memcmp(wa_info[i].oem_table_id, tbl->oem_table_id, ACPI_OEM_TABLE_ID_SIZE) &&
> + wa_info[i].oem_revision == tbl->oem_revision) {
> + apply_id_count_workaround = true;
> + pr_warn(FW_BUG "ID count for ID mapping entry is wrong, applying workaround\n");
> + break;
> + }
> + }
> +}
> +
> static int iort_id_map(struct acpi_iort_id_mapping *map, u8 type, u32 rid_in,
> u32 *rid_out)
> {
> @@ -314,9 +350,21 @@ static int iort_id_map(struct acpi_iort_id_mapping *map, u8 type, u32 rid_in,
> return -ENXIO;
> }
>
> - if (rid_in < map->input_base ||
> - (rid_in >= map->input_base + map->id_count))
> - return -ENXIO;
> + /*
> + * IORT spec says Number of IDs = The number of IDs in the range minus
> + * one, but the IORT code ingored the "minus one", and some firmware
> + * did that too, so apply a workaround here to keep compatible with
> + * both new and old versions of the firmware.
> + */
> + if (apply_id_count_workaround) {
> + if (rid_in < map->input_base ||
> + (rid_in >= map->input_base + map->id_count))
> + return -ENXIO;
> + } else {
> + if (rid_in < map->input_base ||
> + (rid_in > map->input_base + map->id_count))
> + return -ENXIO;
> + }

This seems needlessly repetitive and convoluted... how about refactoring
to something like:

map_max = map->input_base + map->id_count;
if (apply_id_count_workaround)
map_max--;

?

Robin.

> *rid_out = map->output_base + (rid_in - map->input_base);
> return 0;
> @@ -1631,5 +1679,6 @@ void __init acpi_iort_init(void)
> return;
> }
>
> + iort_check_id_count_workaround(iort_table);
> iort_init_platform_devices();
> }
>