[v2] media: mxl5xx: Move xpt structures off stack

Commit Message

Nathan Chancellor March 5, 2024, 10:49 p.m. UTC

When building for LoongArch with clang 18.0.0, the stack usage of
probe() is larger than the allowed 2048 bytes:

  drivers/media/dvb-frontends/mxl5xx.c:1698:12: warning: stack frame size (2368) exceeds limit (2048) in 'probe' [-Wframe-larger-than]
   1698 | static int probe(struct mxl *state, struct mxl5xx_cfg *cfg)
        |            ^
  1 warning generated.

This is the result of the linked LLVM commit, which changes how the
arrays of structures in config_ts() get handled with
CONFIG_INIT_STACK_ZERO and CONFIG_INIT_STACK_PATTERN, which causes the
above warning in combination with inlining, as config_ts() gets inlined
into probe().

This warning can be easily fixed by moving the array of structures off
of the stack via 'static const', which is a better location for these
variables anyways because they are static data that is only ever read
from, never modified, so allocating the stack space is wasteful.

This drops the stack usage from 2368 bytes to 256 bytes with the same
compiler and configuration.

Cc: [e-mail]
Closes: https://github.com/ClangBuiltLinux/linux/issues/1978
Link: https://github.com/llvm/llvm-project/commit/afe8b93ffdfef5d8879e1894b9d7dda40dee2b8d
Reviewed-by: Miguel Ojeda <[e-mail]>
Tested-by: Miguel Ojeda <[e-mail]>
Signed-off-by: Nathan Chancellor <[e-mail]>
---
Changes in v2:
- Rebase on latest media tree
- Fix typo and link in the commit message (Miguel)
- Pick up Miguel's reviewed-by and tested-by tags
- Link to v1: https://lore.kernel.org/r/[e-mail]
---
 drivers/media/dvb-frontends/mxl5xx.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)


---
base-commit: 8c64f4cdf4e6cc5682c52523713af8c39c94e6d5
change-id: 20240111-dvb-mxl5xx-move-structs-off-stack-e12172b1ef02

Best regards,

Patch

diff --git a/drivers/media/dvb-frontends/mxl5xx.c b/drivers/media/dvb-frontends/mxl5xx.c
index 4ebbcf05cc09..91e9c378397c 100644
--- a/drivers/media/dvb-frontends/mxl5xx.c
+++ b/drivers/media/dvb-frontends/mxl5xx.c
@@ -1381,57 +1381,57 @@  static int config_ts(struct mxl *state, enum MXL_HYDRA_DEMOD_ID_E demod_id,
 	u32 nco_count_min = 0;
 	u32 clk_type = 0;
 
-	struct MXL_REG_FIELD_T xpt_sync_polarity[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_sync_polarity[MXL_HYDRA_DEMOD_MAX] = {
 		{0x90700010, 8, 1}, {0x90700010, 9, 1},
 		{0x90700010, 10, 1}, {0x90700010, 11, 1},
 		{0x90700010, 12, 1}, {0x90700010, 13, 1},
 		{0x90700010, 14, 1}, {0x90700010, 15, 1} };
-	struct MXL_REG_FIELD_T xpt_clock_polarity[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_clock_polarity[MXL_HYDRA_DEMOD_MAX] = {
 		{0x90700010, 16, 1}, {0x90700010, 17, 1},
 		{0x90700010, 18, 1}, {0x90700010, 19, 1},
 		{0x90700010, 20, 1}, {0x90700010, 21, 1},
 		{0x90700010, 22, 1}, {0x90700010, 23, 1} };
-	struct MXL_REG_FIELD_T xpt_valid_polarity[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_valid_polarity[MXL_HYDRA_DEMOD_MAX] = {
 		{0x90700014, 0, 1}, {0x90700014, 1, 1},
 		{0x90700014, 2, 1}, {0x90700014, 3, 1},
 		{0x90700014, 4, 1}, {0x90700014, 5, 1},
 		{0x90700014, 6, 1}, {0x90700014, 7, 1} };
-	struct MXL_REG_FIELD_T xpt_ts_clock_phase[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_ts_clock_phase[MXL_HYDRA_DEMOD_MAX] = {
 		{0x90700018, 0, 3}, {0x90700018, 4, 3},
 		{0x90700018, 8, 3}, {0x90700018, 12, 3},
 		{0x90700018, 16, 3}, {0x90700018, 20, 3},
 		{0x90700018, 24, 3}, {0x90700018, 28, 3} };
-	struct MXL_REG_FIELD_T xpt_lsb_first[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_lsb_first[MXL_HYDRA_DEMOD_MAX] = {
 		{0x9070000C, 16, 1}, {0x9070000C, 17, 1},
 		{0x9070000C, 18, 1}, {0x9070000C, 19, 1},
 		{0x9070000C, 20, 1}, {0x9070000C, 21, 1},
 		{0x9070000C, 22, 1}, {0x9070000C, 23, 1} };
-	struct MXL_REG_FIELD_T xpt_sync_byte[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_sync_byte[MXL_HYDRA_DEMOD_MAX] = {
 		{0x90700010, 0, 1}, {0x90700010, 1, 1},
 		{0x90700010, 2, 1}, {0x90700010, 3, 1},
 		{0x90700010, 4, 1}, {0x90700010, 5, 1},
 		{0x90700010, 6, 1}, {0x90700010, 7, 1} };
-	struct MXL_REG_FIELD_T xpt_enable_output[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_enable_output[MXL_HYDRA_DEMOD_MAX] = {
 		{0x9070000C, 0, 1}, {0x9070000C, 1, 1},
 		{0x9070000C, 2, 1}, {0x9070000C, 3, 1},
 		{0x9070000C, 4, 1}, {0x9070000C, 5, 1},
 		{0x9070000C, 6, 1}, {0x9070000C, 7, 1} };
-	struct MXL_REG_FIELD_T xpt_err_replace_sync[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_err_replace_sync[MXL_HYDRA_DEMOD_MAX] = {
 		{0x9070000C, 24, 1}, {0x9070000C, 25, 1},
 		{0x9070000C, 26, 1}, {0x9070000C, 27, 1},
 		{0x9070000C, 28, 1}, {0x9070000C, 29, 1},
 		{0x9070000C, 30, 1}, {0x9070000C, 31, 1} };
-	struct MXL_REG_FIELD_T xpt_err_replace_valid[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_err_replace_valid[MXL_HYDRA_DEMOD_MAX] = {
 		{0x90700014, 8, 1}, {0x90700014, 9, 1},
 		{0x90700014, 10, 1}, {0x90700014, 11, 1},
 		{0x90700014, 12, 1}, {0x90700014, 13, 1},
 		{0x90700014, 14, 1}, {0x90700014, 15, 1} };
-	struct MXL_REG_FIELD_T xpt_continuous_clock[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_continuous_clock[MXL_HYDRA_DEMOD_MAX] = {
 		{0x907001D4, 0, 1}, {0x907001D4, 1, 1},
 		{0x907001D4, 2, 1}, {0x907001D4, 3, 1},
 		{0x907001D4, 4, 1}, {0x907001D4, 5, 1},
 		{0x907001D4, 6, 1}, {0x907001D4, 7, 1} };
-	struct MXL_REG_FIELD_T xpt_nco_clock_rate[MXL_HYDRA_DEMOD_MAX] = {
+	static const struct MXL_REG_FIELD_T xpt_nco_clock_rate[MXL_HYDRA_DEMOD_MAX] = {
 		{0x90700044, 16, 80}, {0x90700044, 16, 81},
 		{0x90700044, 16, 82}, {0x90700044, 16, 83},
 		{0x90700044, 16, 84}, {0x90700044, 16, 85},