Re: [PATCH 4/4] serial: Allow unaligned i/o access

[Michael S. Tsirkin]

On Thu, Sep 08, 2022 at 02:11:28PM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Wed, Sep 7, 2022 at 2:03 AM Arwed Meyer <arwed.meyer@gmx.de> wrote:
> 
>     Unaligned i/o access on serial UART works on real PCs.
>     This is used for example by FreeDOS CTMouse driver. Without this it
>     can't reset and detect serial mice.
> 
>     Resolves: https://gitlab.com/qemu-project/qemu/-/issues/77
>     Signed-off-by: Arwed Meyer <arwed.meyer@gmx.de>
>     ---
>      hw/char/serial.c | 3 +++
>      1 file changed, 3 insertions(+)
> 
>     diff --git a/hw/char/serial.c b/hw/char/serial.c
>     index 7061aacbce..41b5e61977 100644
>     --- a/hw/char/serial.c
>     +++ b/hw/char/serial.c
>     @@ -961,6 +961,9 @@ void serial_set_frequency(SerialState *s, uint32_t
>     frequency)
>      const MemoryRegionOps serial_io_ops = {
>          .read = serial_ioport_read,
>          .write = serial_ioport_write,
>     +    .valid = {
>     +        .unaligned = 1,
>     +    },
> 
> 
> I don't get how this can help if both min_access_size & max_access_size are 1.
>  
> 
>          .impl = {
>              .min_access_size = 1,
>              .max_access_size = 1,
>     --
>     2.34.1


Because that's .impl. If access is invalid we don't get as far
as breaking it up to chunks.

> 
> 
> 
> 
> --
> Marc-André Lureau