Re: [PATCH] hw/nvram: at24 return 0xff if 1 byte address

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Hi Patrick,

On 12/20/21 01:32, Patrick Venture wrote:
> The at24 eeproms are 2 byte devices that return 0xff when they are read
> from with a partial (1-byte) address written.  This distinction was
> found comparing model behavior to real hardware testing.
> 
> Tested: `i2ctransfer -f -y 45 w1@85 0 r1` returns 0xff instead of next
> byte
> 
> Signed-off-by: Patrick Venture <venture@google.com>
> ---
>  hw/nvram/eeprom_at24c.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/nvram/eeprom_at24c.c b/hw/nvram/eeprom_at24c.c
> index a9e3702b00..184fac9702 100644
> --- a/hw/nvram/eeprom_at24c.c
> +++ b/hw/nvram/eeprom_at24c.c
> @@ -62,7 +62,9 @@ int at24c_eeprom_event(I2CSlave *s, enum i2c_event event)
>      case I2C_START_SEND:
>      case I2C_START_RECV:
>      case I2C_FINISH:
> -        ee->haveaddr = 0;
> +        if (event != I2C_START_RECV) {
> +            ee->haveaddr = 0;
> +        }

Alternatively (matter of taste, I find it easier to read):

       case I2C_START_SEND:
       case I2C_FINISH:
           ee->haveaddr = 0;
           /* fallthrough */
       case I2C_START_RECV:

>          DPRINTK("clear\n");
>          if (ee->blk && ee->changed) {
>              int len = blk_pwrite(ee->blk, 0, ee->mem, ee->rsize, 0);
> @@ -86,6 +88,10 @@ uint8_t at24c_eeprom_recv(I2CSlave *s)
>      EEPROMState *ee = AT24C_EE(s);
>      uint8_t ret;
>  
> +    if (ee->haveaddr == 1) {
> +        return 0xff;

Don't we need to increase ee->haveaddr?

> +    }
> +
>      ret = ee->mem[ee->cur];
>  
>      ee->cur = (ee->cur + 1u) % ee->rsize;

Here for parity with send, what about:

    if (ee->haveaddr < 2) {
        ret = 0xff;
        ee->haveaddr++;
    } else {
        ret = ee->mem[ee->cur];
        ee->cur = (ee->cur + 1u) % ee->rsize;
    }

?