Re: [RFC PATCH 4/6] dp8393x: Store CAM registers as 16-bit

[Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>]

On 03/07/2021 15:19, Philippe Mathieu-Daudé wrote:

> Per the DP83932C datasheet from July 1995:
> 
>    4.0 SONIC Registers
>    4.1 THE CAM UNIT
> 
>      The Content Addressable Memory (CAM) consists of sixteen
>      48-bit entries for complete address filtering of network
>      packets. Each entry corresponds to a 48-bit destination
>      address that is user programmable and can contain any
>      combination of Multicast or Physical addresses. Each entry
>      is partitioned into three 16-bit CAM cells accessible
>      through CAM Address Ports (CAP 2, CAP 1 and CAP 0) with
>      CAP0 corresponding to the least significant 16 bits of
>      the Destination Address and CAP2 corresponding to the
>      most significant bits.
> 
> Store the CAM registers as 16-bit as it simplifies the code.
> There is no change in the migration stream.
> 
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>   hw/net/dp8393x.c | 23 ++++++++++-------------
>   1 file changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/hw/net/dp8393x.c b/hw/net/dp8393x.c
> index c9b478c127c..e0055b178b1 100644
> --- a/hw/net/dp8393x.c
> +++ b/hw/net/dp8393x.c
> @@ -157,7 +157,7 @@ struct dp8393xState {
>       MemoryRegion mmio;
>   
>       /* Registers */
> -    uint8_t cam[16][6];
> +    uint16_t cam[16][3];
>       uint16_t regs[0x40];
>   
>       /* Temporaries */
> @@ -280,15 +280,13 @@ static void dp8393x_do_load_cam(dp8393xState *s)
>           address_space_read(&s->as, dp8393x_cdp(s),
>                              MEMTXATTRS_UNSPECIFIED, s->data, size);
>           index = dp8393x_get(s, width, 0) & 0xf;
> -        s->cam[index][0] = dp8393x_get(s, width, 1) & 0xff;
> -        s->cam[index][1] = dp8393x_get(s, width, 1) >> 8;
> -        s->cam[index][2] = dp8393x_get(s, width, 2) & 0xff;
> -        s->cam[index][3] = dp8393x_get(s, width, 2) >> 8;
> -        s->cam[index][4] = dp8393x_get(s, width, 3) & 0xff;
> -        s->cam[index][5] = dp8393x_get(s, width, 3) >> 8;
> -        trace_dp8393x_load_cam(index, s->cam[index][0], s->cam[index][1],
> -                               s->cam[index][2], s->cam[index][3],
> -                               s->cam[index][4], s->cam[index][5]);
> +        s->cam[index][0] = dp8393x_get(s, width, 1);
> +        s->cam[index][1] = dp8393x_get(s, width, 2);
> +        s->cam[index][2] = dp8393x_get(s, width, 3);
> +        trace_dp8393x_load_cam(index,
> +                               s->cam[index][0] >> 8, s->cam[index][0] & 0xff,
> +                               s->cam[index][1] >> 8, s->cam[index][1] & 0xff,
> +                               s->cam[index][2] >> 8, s->cam[index][2] & 0xff);
>           /* Move to next entry */
>           s->regs[SONIC_CDC]--;
>           s->regs[SONIC_CDP] += size;
> @@ -591,8 +589,7 @@ static uint64_t dp8393x_read(void *opaque, hwaddr addr, unsigned int size)
>       case SONIC_CAP1:
>       case SONIC_CAP0:
>           if (s->regs[SONIC_CR] & SONIC_CR_RST) {
> -            val = s->cam[s->regs[SONIC_CEP] & 0xf][2 * (SONIC_CAP0 - reg) + 1] << 8;
> -            val |= s->cam[s->regs[SONIC_CEP] & 0xf][2 * (SONIC_CAP0 - reg)];
> +            val = s->cam[s->regs[SONIC_CEP] & 0xf][2 * (SONIC_CAP0 - reg)];
>           }
>           break;
>       /* All other registers have no special contraints */
> @@ -987,7 +984,7 @@ static const VMStateDescription vmstate_dp8393x = {
>       .version_id = 0,
>       .minimum_version_id = 0,
>       .fields = (VMStateField []) {
> -        VMSTATE_BUFFER_UNSAFE(cam, dp8393xState, 0, 16 * 6),
> +        VMSTATE_BUFFER_UNSAFE(cam, dp8393xState, 0, 16 * 3 * 2),
>           VMSTATE_UINT16_ARRAY(regs, dp8393xState, 0x40),
>           VMSTATE_END_OF_LIST()
>       }

I need to do some testing first to make sure dp8393x_get() and dp8393x_put() are 
doing the right thing here, but it looks correct.

Also given that the migration stream for MIPS machines has been broken for many years 
until your latest PR, I would have no objection if you wanted to change 
VMSTATE_BUFFER_UNSAFE to VMSTATE_UINT16_ARRAY.


ATB,

Mark.