[PATCH] riscv: thead: fix D-cache flushing

[PATCH] riscv: thead: fix D-cache flushing

[Han Gao]

Use CIPA instead of CPA to clean and invalidate cache lines. This
fixes stale DMA descriptors breaking USB enumeration on TH1520.

Signed-off-by: Han Gao <gaohan@iscas.ac.cn>
---
 arch/riscv/lib/thead_cmo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/lib/thead_cmo.c b/arch/riscv/lib/thead_cmo.c
index b8051e29e02b..763ff799eddd 100644
--- a/arch/riscv/lib/thead_cmo.c
+++ b/arch/riscv/lib/thead_cmo.c
@@ -40,6 +40,6 @@ void flush_dcache_range(unsigned long start, unsigned long end)
 {
 	register unsigned long i asm("a0") = start & ~(CONFIG_SYS_CACHELINE_SIZE - 1);
 	for (; i < end; i += CONFIG_SYS_CACHELINE_SIZE)
-		__asm__ __volatile__(DCACHE_CPA_A0);
+		__asm__ __volatile__(DCACHE_CIPA_A0);
 	__asm__ __volatile__(SYNC_S);
 }

---
base-commit: 211de43d0f954a00a490220c1aac9db298287c40
change-id: 20260919-fixcmo-cf56064fccd6

Best regards,
--  
Han Gao <gaohan@iscas.ac.cn>

Re: [PATCH] riscv: thead: fix D-cache flushing

[Yixun Lan]

Hi Han,


On 04:29 Sat 19 Sep     , Han Gao wrote:
> Use CIPA instead of CPA to clean and invalidate cache lines. This
> fixes stale DMA descriptors breaking USB enumeration on TH1520.
> 
I suspect this isn't a correct fix, there are separate functions for dcache
flush and invalidate - flush_dcache_range() vs invalidate_dcache_range()

Better to check the USB driver, where it actually need to flush or invalidate?

> Signed-off-by: Han Gao <gaohan@iscas.ac.cn>
> ---
>  arch/riscv/lib/thead_cmo.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/lib/thead_cmo.c b/arch/riscv/lib/thead_cmo.c
> index b8051e29e02b..763ff799eddd 100644
> --- a/arch/riscv/lib/thead_cmo.c
> +++ b/arch/riscv/lib/thead_cmo.c
> @@ -40,6 +40,6 @@ void flush_dcache_range(unsigned long start, unsigned long end)
>  {
>  	register unsigned long i asm("a0") = start & ~(CONFIG_SYS_CACHELINE_SIZE - 1);
>  	for (; i < end; i += CONFIG_SYS_CACHELINE_SIZE)
> -		__asm__ __volatile__(DCACHE_CPA_A0);
> +		__asm__ __volatile__(DCACHE_CIPA_A0);
>  	__asm__ __volatile__(SYNC_S);
>  }
> 
> ---
> base-commit: 211de43d0f954a00a490220c1aac9db298287c40
> change-id: 20260919-fixcmo-cf56064fccd6
> 
> Best regards,
> --  
> Han Gao <gaohan@iscas.ac.cn>
> 

-- 
Yixun Lan (dlan)

Re: [PATCH] riscv: thead: fix D-cache flushing

[Yao Zi]

On Sat, Sep 19, 2026 at 04:29:41AM +0800, Han Gao wrote:
> Use CIPA instead of CPA to clean and invalidate cache lines. This
> fixes stale DMA descriptors breaking USB enumeration on TH1520.

I guess this issue isn't present in mainline U-Boot yet, since we don't
have USB support for TH1520 currently? If so, please omit this part in
commit message, you could mention this below the --- line.

And it would be good to mention the meaning and full form
("th.dcache.*") of CPA/CIPA here, and attach a link to the documentation
of T-Head's extensions. As a fix, this also deserves a Fixes tag.

For the fix itself, it sounds correct. I had a brief look over several
architectures' flush_dcache_range(),

- The zicbom path on RISC-V makes use of cbo.flush, per the RISC-V
  specification (Volume I, 19.6.1 Cache-Block Management Instructions),
  a flush operation atomically performs a clean operation followed by an
  invalidate operation.
- MIPS uses HIT_WRITEBACK_INV_D & HIT_WRITEBACK_INV_SD
- PowerPC implements flush_dcache_range() with dcbf, which is described
  as "those locations are written to main storage and additional
  locations in the block may be written to main storage. The block is
  invalidated in the data caches of all/this (depending on memory
  coherence) processors", matching the behavior of flush
  (clean/writeback & invalidate).
  - flush_dcache_range() is no-op on platforms other than
    MPC85xx/MPC86xx, I guess coherency is guaranteed otherwise?
- ARMv8's flush_dcache_range() is also commented as "INvalidates range
  in all levels of D-cache/unified cache"

So this fix aligns thead_cmo.c's behavior with other implementations.
With the commit message improved,

Reviewed-by: Yao Zi <me@ziyao.cc>

> Signed-off-by: Han Gao <gaohan@iscas.ac.cn>
> ---
>  arch/riscv/lib/thead_cmo.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/lib/thead_cmo.c b/arch/riscv/lib/thead_cmo.c
> index b8051e29e02b..763ff799eddd 100644
> --- a/arch/riscv/lib/thead_cmo.c
> +++ b/arch/riscv/lib/thead_cmo.c
> @@ -40,6 +40,6 @@ void flush_dcache_range(unsigned long start, unsigned long end)
>  {
>  	register unsigned long i asm("a0") = start & ~(CONFIG_SYS_CACHELINE_SIZE - 1);
>  	for (; i < end; i += CONFIG_SYS_CACHELINE_SIZE)
> -		__asm__ __volatile__(DCACHE_CPA_A0);
> +		__asm__ __volatile__(DCACHE_CIPA_A0);
>  	__asm__ __volatile__(SYNC_S);
>  }

Regards,
Yao Zi

Re: [PATCH] riscv: thead: fix D-cache flushing

[Yao Zi]

On Sun, Sep 20, 2026 at 12:56:09AM +0000, Yixun Lan wrote:
> Hi Han,
> 
> 
> On 04:29 Sat 19 Sep     , Han Gao wrote:
> > Use CIPA instead of CPA to clean and invalidate cache lines. This
> > fixes stale DMA descriptors breaking USB enumeration on TH1520.
> > 
> I suspect this isn't a correct fix, there are separate functions for dcache
> flush and invalidate - flush_dcache_range() vs invalidate_dcache_range()
> 
> Better to check the USB driver, where it actually need to flush or invalidate?

Whether the USB driver needs a flush or only invalidation or not, the
current thead_cmo.c only cleans the cacheline in flush_dcache_range(),
which is wrong.

But out of curiosity, I have a look at DWC3, and found at least the call
in dwc3_ep0_start_trans() requires dwc3_flush_dcache(), which is a
wrapper over flush_dcache_range(), to really clean the cache, otherwise
the DMA data and TRB might not be visible to an incoherent DWC3.

> > Signed-off-by: Han Gao <gaohan@iscas.ac.cn>

Regards,
Yao Zi