To fully isolate FPU operations in a single place, we must avoid
situations where compilers spill FP values to registers due to FP enable
in a specific C file. Note that even if we isolate all FPU functions in
a single file and call its interface from other files, the compiler
might enable the use of FPU before we call DC_FP_START. Nevertheless, it
is the programmer's responsibility to invoke DC_FP_START/END in the
correct place. To highlight situations where developers forgot to use
the FP protection before calling the DC FPU interface functions, we
introduce a helper that checks if the function is invoked under FP
protection. If not, it will trigger a kernel warning.
Changes cince V2 (Christian):
- Do not use this_cpu_* between get/put_cpu_ptr().
- In the kernel documentation, better describe restrictions.
- Make dc_assert_fp_enabled trigger the ASSERT message.
Changes since V1:
- Remove fp_enable variables
- Rename dc_is_fp_enabled to dc_assert_fp_enabled
- Replace wrong variable type
Cc: Harry Wentland <harry.wentland@xxxxxxx>
Cc: Anson Jacob <Anson.Jacob@xxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Hersen Wu <hersenxs.wu@xxxxxxx>
Cc: Aric Cyr <aric.cyr@xxxxxxx>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@xxxxxxx>
---
.../gpu/drm/amd/display/amdgpu_dm/dc_fpu.c | 19 +++++++++++++++++++
.../gpu/drm/amd/display/amdgpu_dm/dc_fpu.h | 1 +
.../drm/amd/display/dc/dcn20/dcn20_resource.c | 2 ++
.../drm/amd/display/dc/fpu_operations/dcn2x.c | 18 ++++++++++++++++++
4 files changed, 40 insertions(+)
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
index d0d3e8a34db5..107e1c50576e 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
@@ -41,6 +41,25 @@
static DEFINE_PER_CPU(int, fpu_recursion_depth);
+/**
+ * dc_assert_fp_enabled - Check if FPU protection is enabled
+ *
+ * This function tells if the code is already under FPU protection or not. A
+ * function that works as an API for a set of FPU operations can use this
+ * function for checking if the caller invoked it after DC_FP_START(). For
+ * example, take a look at dcn2x.c file.
+ */
+inline void dc_assert_fp_enabled(void)
+{
+ int *pcpu, depth = 0;
+
+ pcpu = get_cpu_ptr(&fpu_recursion_depth);
+ depth = *pcpu;
+ put_cpu_ptr(&fpu_recursion_depth);
+
+ ASSERT(depth > 1);
+}
+
/**
* dc_fpu_begin - Enables FPU protection
* @function_name: A string containing the function name for debug purposes
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h
index fb54983c5c60..b8275b397920 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h
@@ -27,6 +27,7 @@
#ifndef __DC_FPU_H__
#define __DC_FPU_H__
+void dc_assert_fp_enabled(void);
void dc_fpu_begin(const char *function_name, const int line);
void dc_fpu_end(const char *function_name, const int line);
diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
index f99b09643a52..d0b34c7f99dc 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
@@ -2355,7 +2355,9 @@ int dcn20_populate_dml_pipes_from_context(
}
/* populate writeback information */
+ DC_FP_START();
dc->res_pool->funcs->populate_dml_writeback_from_context(dc, res_ctx, pipes);
+ DC_FP_END();
return pipe_cnt;
}
diff --git a/drivers/gpu/drm/amd/display/dc/fpu_operations/dcn2x.c b/drivers/gpu/drm/amd/display/dc/fpu_operations/dcn2x.c
index 95a0b89302a9..3ea90090264c 100644
--- a/drivers/gpu/drm/amd/display/dc/fpu_operations/dcn2x.c
+++ b/drivers/gpu/drm/amd/display/dc/fpu_operations/dcn2x.c
@@ -43,6 +43,22 @@
* that deals with FP register is contained within this call.
* 3. All function that needs to be accessed outside this file requires a
* public interface that not uses any FPU reference.
+ * 4. Developers **must not** use DC_FP_START/END in this file, but they need
+ * to ensure that the caller invokes it before access any function available
+ * in this file. For this reason, public functions in this file must invoke
+ * dc_assert_fp_enabled();
+ *
+ * Let's expand a little bit more the idea in the code pattern. To fully
+ * isolate FPU operations in a single place, we must avoid situations where
+ * compilers spill FP values to registers due to FP enable in a specific C
+ * file. Note that even if we isolate all FPU functions in a single file and
+ * call its interface from other files, the compiler might enable the use of
+ * FPU before we call DC_FP_START. Nevertheless, it is the programmer's
+ * responsibility to invoke DC_FP_START/END in the correct place. To highlight
+ * situations where developers forgot to use the FP protection before calling
+ * the DC FPU interface functions, we introduce a helper that checks if the
+ * function is invoked under FP protection. If not, it will trigger a kernel
+ * warning.
*/
void dcn20_populate_dml_writeback_from_context(struct dc *dc,
@@ -51,6 +67,8 @@ void dcn20_populate_dml_writeback_from_context(struct dc *dc,
{
int pipe_cnt, i;
+ dc_assert_fp_enabled();
+
for (i = 0, pipe_cnt = 0; i < dc->res_pool->pipe_count; i++) {
struct dc_writeback_info *wb_info = &res_ctx->pipe_ctx[i].stream->writeback_info[0];
--
2.25.1
