[PATCH v3 13/35] acpigen: Support writing a length
Bin Meng
bmeng.cn at gmail.com
Mon Jun 29 03:27:47 CEST 2020
On Sun, Jun 14, 2020 at 10:55 AM Simon Glass <sjg at chromium.org> wrote:
>
> It is convenient to write a length value for preceding a block of data.
> Of course the length is not known or is hard to calculate a priori. So add
> a way to mark the start on a stack, so the length can be updated when
> known.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> Reviewed-by: Wolfgang Wallner <wolfgang.wallner at br-automation.com>
> ---
>
> Changes in v3:
> - Add a reference to the ACPI spec
> - Add a define for the 0x80 constant
> - Move the function comments into this patch
>
> include/acpi/acpigen.h | 38 +++++++++++++++++++++++++
> include/dm/acpi.h | 7 +++++
> lib/acpi/acpigen.c | 33 ++++++++++++++++++++++
> test/dm/acpigen.c | 64 ++++++++++++++++++++++++++++++++++++++++--
> 4 files changed, 140 insertions(+), 2 deletions(-)
>
> diff --git a/include/acpi/acpigen.h b/include/acpi/acpigen.h
> index 7365cce738..12cd1bd578 100644
> --- a/include/acpi/acpigen.h
> +++ b/include/acpi/acpigen.h
> @@ -14,6 +14,9 @@
>
> struct acpi_ctx;
>
> +/* Top 4 bits of the value used to indicate a three-byte length value */
> +#define ACPI_PKG_LEN_3_BYTES 0x80
> +
> /**
> * acpigen_get_current() - Get the current ACPI code output pointer
> *
> @@ -65,4 +68,39 @@ void acpigen_emit_stream(struct acpi_ctx *ctx, const char *data, int size);
> */
> void acpigen_emit_string(struct acpi_ctx *ctx, const char *str);
>
> +/**
> + * acpigen_write_len_f() - Write a 'forward' length placeholder
> + *
> + * This adds space for a length value in the ACPI stream and pushes the current
> + * position (before the length) on the stack. After calling this you can write
> + * some data and then call acpigen_pop_len() to update the length value.
> + *
> + * Usage:
> + *
> + * acpigen_write_len_f() ------\
> + * acpigen_write...() |
> + * acpigen_write...() |
> + * acpigen_write_len_f() --\ |
> + * acpigen_write...() | |
> + * acpigen_write...() | |
> + * acpigen_pop_len() ------/ |
> + * acpigen_write...() |
> + * acpigen_pop_len() ----------/
> + *
> + * See ACPI 6.3 section 20.2.4 Package Length Encoding
It's better we put some more comments here mentioning that we are
hardcoding a 3 byte packet length encoding that can represent up to
2*20 packet length in total.
Any chance to optimize this routine not to use a hardcode 3 byte encoding?
> + *
> + * @ctx: ACPI context pointer
> + */
> +void acpigen_write_len_f(struct acpi_ctx *ctx);
> +
> +/**
> + * acpigen_pop_len() - Update the previously stacked length placeholder
> + *
> + * Call this after the data for the block gas been written. It updates the
typo: gas -> has
> + * top length value in the stack and pops it off.
> + *
> + * @ctx: ACPI context pointer
> + */
> +void acpigen_pop_len(struct acpi_ctx *ctx);
> +
> #endif
> diff --git a/include/dm/acpi.h b/include/dm/acpi.h
> index 696b1a96a0..f27ca64507 100644
> --- a/include/dm/acpi.h
> +++ b/include/dm/acpi.h
> @@ -22,6 +22,9 @@
> /* Length of an ACPI name string including nul terminator */
nits: nul -> null
> #define ACPI_NAME_MAX (ACPI_NAME_LEN + 1)
>
> +/* Number of nested objects supported */
> +#define ACPIGEN_LENSTACK_SIZE 10
> +
> #if !defined(__ACPI__)
>
> /**
> @@ -35,6 +38,8 @@
> * adding a new table. The RSDP holds pointers to the RSDT and XSDT.
> * @rsdt: Pointer to the Root System Description Table
> * @xsdt: Pointer to the Extended System Description Table
> + * @len_stack: Stack of 'length' words to fix up later
> + * @ltop: Points to current top of stack (0 = empty)
> */
> struct acpi_ctx {
> void *base;
> @@ -42,6 +47,8 @@ struct acpi_ctx {
> struct acpi_rsdp *rsdp;
> struct acpi_rsdt *rsdt;
> struct acpi_xsdt *xsdt;
> + char *len_stack[ACPIGEN_LENSTACK_SIZE];
> + int ltop;
> };
>
> /**
> diff --git a/lib/acpi/acpigen.c b/lib/acpi/acpigen.c
> index 1223f0d1c4..2c2b604d80 100644
> --- a/lib/acpi/acpigen.c
> +++ b/lib/acpi/acpigen.c
> @@ -10,6 +10,7 @@
>
> #include <common.h>
> #include <dm.h>
> +#include <log.h>
> #include <acpi/acpigen.h>
> #include <dm/acpi.h>
>
> @@ -37,6 +38,38 @@ void acpigen_emit_dword(struct acpi_ctx *ctx, uint data)
> acpigen_emit_byte(ctx, (data >> 24) & 0xff);
> }
>
> +/*
> + * Maximum length for an ACPI object generated by this code,
> + *
> + * If you need to change this, change acpigen_write_len_f(ctx) and
> + * acpigen_pop_len(ctx)
> + */
> +#define ACPIGEN_MAXLEN 0xfffff
> +
> +void acpigen_write_len_f(struct acpi_ctx *ctx)
> +{
> + assert(ctx->ltop < (ACPIGEN_LENSTACK_SIZE - 1));
> + ctx->len_stack[ctx->ltop++] = ctx->current;
> + acpigen_emit_byte(ctx, 0);
> + acpigen_emit_byte(ctx, 0);
> + acpigen_emit_byte(ctx, 0);
> +}
> +
> +void acpigen_pop_len(struct acpi_ctx *ctx)
> +{
> + int len;
> + char *p;
> +
> + assert(ctx->ltop > 0);
> + p = ctx->len_stack[--ctx->ltop];
> + len = ctx->current - (void *)p;
> + assert(len <= ACPIGEN_MAXLEN);
> + /* generate store length for 0xfffff max */
> + p[0] = ACPI_PKG_LEN_3_BYTES | (len & 0xf);
> + p[1] = len >> 4 & 0xff;
> + p[2] = len >> 12 & 0xff;
> +}
> +
> void acpigen_emit_stream(struct acpi_ctx *ctx, const char *data, int size)
> {
> int i;
> diff --git a/test/dm/acpigen.c b/test/dm/acpigen.c
> index 571510722d..71f70ebf71 100644
> --- a/test/dm/acpigen.c
> +++ b/test/dm/acpigen.c
> @@ -22,7 +22,7 @@
> #define TEST_STRING "frogmore"
> #define TEST_STREAM2 "\xfa\xde"
>
> -static int alloc_context(struct acpi_ctx **ctxp)
> +static int alloc_context_size(struct acpi_ctx **ctxp, int size)
> {
> struct acpi_ctx *ctx;
>
> @@ -30,17 +30,23 @@ static int alloc_context(struct acpi_ctx **ctxp)
> ctx = malloc(sizeof(*ctx));
> if (!ctx)
> return -ENOMEM;
> - ctx->base = malloc(150);
> + ctx->base = malloc(size);
> if (!ctx->base) {
> free(ctx);
> return -ENOMEM;
> }
> + ctx->ltop = 0;
> ctx->current = ctx->base;
> *ctxp = ctx;
>
> return 0;
> }
>
> +static int alloc_context(struct acpi_ctx **ctxp)
> +{
> + return alloc_context_size(ctxp, 150);
> +}
> +
> static void free_context(struct acpi_ctx **ctxp)
> {
> free((*ctxp)->base);
> @@ -338,3 +344,57 @@ static int dm_test_acpi_spi(struct unit_test_state *uts)
> return 0;
> }
> DM_TEST(dm_test_acpi_spi, DM_TESTF_SCAN_PDATA | DM_TESTF_SCAN_FDT);
> +
> +/**
> + * get_length() - decode a three-byte length field
> + *
> + * @ptr: Length encoded as per ACPI
> + * @return decoded length, or -EINVAL on error
> + */
> +static int get_length(u8 *ptr)
> +{
> + if (!(*ptr & 0x80))
> + return -EINVAL;
> +
> + return (*ptr & 0xf) | ptr[1] << 4 | ptr[2] << 12;
> +}
> +
> +/* Test emitting a length */
> +static int dm_test_acpi_len(struct unit_test_state *uts)
> +{
> + const int size = 0xc0000;
> + struct acpi_ctx *ctx;
> + u8 *ptr;
> + int i;
> +
> + ut_assertok(alloc_context_size(&ctx, size));
> +
> + ptr = acpigen_get_current(ctx);
> +
> + /* Write a byte and a 3-byte length */
> + acpigen_write_len_f(ctx);
> + acpigen_emit_byte(ctx, 0x23);
> + acpigen_pop_len(ctx);
> + ut_asserteq(1 + 3, get_length(ptr));
> +
> + /* Write 200 bytes so we need two length bytes */
> + ptr = ctx->current;
> + acpigen_write_len_f(ctx);
> + for (i = 0; i < 200; i++)
> + acpigen_emit_byte(ctx, 0x23);
> + acpigen_pop_len(ctx);
> + ut_asserteq(200 + 3, get_length(ptr));
> +
> + /* Write 40KB so we need three length bytes */
> + ptr = ctx->current;
> + acpigen_write_len_f(ctx);
> + for (i = 0; i < 40000; i++)
> + acpigen_emit_byte(ctx, 0x23);
> + acpigen_pop_len(ctx);
> + ut_asserteq(40000 + 3, get_length(ptr));
> +
> + free_context(&ctx);
> +
> + return 0;
> +}
> +DM_TEST(dm_test_acpi_len, 0);
Regards,
Bin
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