[RFC] mmc: Remove alignment hole for cmdidx in struct mmc_cmd

[Jonas Karlman]

The alignment hole caused by cmdidx in struct mmc_cmd cause strange
issues together with the peephole2 optimization on Amlogic SoCs.
Following was observed while working on SPL support for Amlogic SoCs.

sd_get_capabilities() normally issue a CMD55 followed by a CMD51.
However, on at least Amlogic S905 (Cortex-A53) and S905X3 (Cortex-A55),
CMD55 was instead followed by CMD8 (and a few reties) in SPL.

Code from the call site:

  cmd.cmdidx = SD_CMD_APP_SEND_SCR; // 51
  ...
  data.blocksize = 8;
  ...
  err = mmc_send_cmd_retry(mmc, &cmd, &data, 3);

Running the code with MMC_TRACE enabled shows:

CMD_SEND:55
                ARG                      0x50480000
                MMC_RSP_R1,5,6,7         0x00000920
CMD_SEND:8
                ARG                      0x00000000
                RET                      -110

Removing the alignment hole by changing cmdidx from ushort to uint or
building with -fno-peephole2 flag seem to resolve this issue.

CMD_SEND:55
                ARG                      0x50480000
                MMC_RSP_R1,5,6,7         0x00000920
CMD_SEND:51
                ARG                      0x00000000
                MMC_RSP_R1,5,6,7         0x00000920

Same issue was observed building U-Boot with gcc 8-13. Please advise on
how to best work around this possible gcc optimization bug.

Signed-off-by: Jonas Karlman <jo...@kwiboo.se>
---
 arch/arm/cpu/armv8/config.mk | 2 ++
 include/mmc.h                | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm/cpu/armv8/config.mk b/arch/arm/cpu/armv8/config.mk
index 4d74b2a533e0..7177dcd7c73b 100644
--- a/arch/arm/cpu/armv8/config.mk
+++ b/arch/arm/cpu/armv8/config.mk
@@ -7,6 +7,8 @@ PLATFORM_RELFLAGS += $(call cc-option,-mbranch-protection=none)
 PF_NO_UNALIGNED := $(call cc-option, -mstrict-align)
 PLATFORM_CPPFLAGS += $(PF_NO_UNALIGNED)
 
+PLATFORM_CPPFLAGS += $(call cc-option,-fno-peephole2)
+
 EFI_LDS := elf_aarch64_efi.lds
 EFI_CRT0 := crt0_aarch64_efi.o
 EFI_RELOC := reloc_aarch64_efi.o
diff --git a/include/mmc.h b/include/mmc.h
index 9aef31ea5deb..7b3868bb5664 100644
--- a/include/mmc.h
+++ b/include/mmc.h
@@ -413,7 +413,7 @@ struct mmc_cid {
 };
 
 struct mmc_cmd {
-       ushort cmdidx;
+       uint cmdidx;
        uint resp_type;
        uint cmdarg;
        uint response[4];
-- 
2.42.0