hw/block/m25p80: Fix Winbond Fast Read dummy cycles

[PATCH] hw/block/m25p80: Fix Winbond Fast Read dummy cycles

Joel Bueno posted 1 patch 1 month, 2 weeks ago

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git fetch https://github.com/patchew-project/qemu tags/patchew/20251221105340.2699327-1-buenocalvachejoel@gmail.com

Maintainers: Alistair Francis <alistair@alistair23.me>, Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>

hw/block/m25p80.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

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[PATCH] hw/block/m25p80: Fix Winbond Fast Read dummy cycles

Posted by Joel Bueno 1 month, 2 weeks ago

The Fast Read (0Bh) instruction requires 8 dummy clock cycles
according to Winbond datasheets (e.g., W25Q256JV Section 8.2.12).
However, the current code adds 8 to needed_bytes, which represents
bytes, not clock cycles. Since 8 clock cycles equals 1 byte in SPI
communication (1 bit per clock edge), this results in 64 dummy
clock cycles instead of 8.

Change the Winbond case to add 1 byte (8 clocks) instead of 8 bytes
(64 clocks), matching the existing implementation for SST flash and
the datasheet specifications.

Signed-off-by: Joel Bueno <buenocalvachejoel@gmail.com>
---
 hw/block/m25p80.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/block/m25p80.c b/hw/block/m25p80.c
index a5336d92ff..21c2118b33 100644
--- a/hw/block/m25p80.c
+++ b/hw/block/m25p80.c
@@ -1001,7 +1001,7 @@ static void decode_fast_read_cmd(Flash *s)
         s->needed_bytes += 1;
         break;
     case MAN_WINBOND:
-        s->needed_bytes += 8;
+        s->needed_bytes += 1;
         break;
     case MAN_NUMONYX:
         s->needed_bytes += numonyx_extract_cfg_num_dummies(s);
-- 
2.51.0

Re: [PATCH] hw/block/m25p80: Fix Winbond Fast Read dummy cycles

Posted by Joel Bueno 1 month ago

Is there any feedback on this patch series?

On Sun, Dec 21, 2025 at 11:53 Joel Bueno <buenocalvachejoel@gmail.com>
wrote:

> The Fast Read (0Bh) instruction requires 8 dummy clock cycles
> according to Winbond datasheets (e.g., W25Q256JV Section 8.2.12).
> However, the current code adds 8 to needed_bytes, which represents
> bytes, not clock cycles. Since 8 clock cycles equals 1 byte in SPI
> communication (1 bit per clock edge), this results in 64 dummy
> clock cycles instead of 8.
>
> Change the Winbond case to add 1 byte (8 clocks) instead of 8 bytes
> (64 clocks), matching the existing implementation for SST flash and
> the datasheet specifications.
>
> Signed-off-by: Joel Bueno <buenocalvachejoel@gmail.com>
> ---
>  hw/block/m25p80.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/block/m25p80.c b/hw/block/m25p80.c
> index a5336d92ff..21c2118b33 100644
> --- a/hw/block/m25p80.c
> +++ b/hw/block/m25p80.c
> @@ -1001,7 +1001,7 @@ static void decode_fast_read_cmd(Flash *s)
>          s->needed_bytes += 1;
>          break;
>      case MAN_WINBOND:
> -        s->needed_bytes += 8;
> +        s->needed_bytes += 1;
>          break;
>      case MAN_NUMONYX:
>          s->needed_bytes += numonyx_extract_cfg_num_dummies(s);
> --
> 2.51.0
>
>