Re: [PATCH 1/2] hw/cxl: Respect Media Operation max ops discovery semantics

[Jonathan Cameron <jonathan.cameron@huawei.com>]

On Wed, 18 Mar 2026 11:55:07 -0700
Davidlohr Bueso <dave@stgolabs.net> wrote:

> The Discovery handler rejects requests where start_index + num_ops
> exceeds the total number of supported operations. Per CXL 4.0
> Table 8-332, num_ops is the "Maximum number of Media Operation to
> return" - a maximum, not an exact count. The device should return
> up to that many entries, not reject the request.
> 
> Cap num_ops to the available entries from start_index instead of
> erroring the command.
> 
> Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
One trivial thing inline.

> ---
>  hw/cxl/cxl-mailbox-utils.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/hw/cxl/cxl-mailbox-utils.c b/hw/cxl/cxl-mailbox-utils.c
> index a3143f3faa23..71a012121c87 100644
> --- a/hw/cxl/cxl-mailbox-utils.c
> +++ b/hw/cxl/cxl-mailbox-utils.c
> @@ -2593,6 +2593,7 @@ static CXLRetCode media_operations_discovery(uint8_t *payload_in,
>      } QEMU_PACKED *media_op_in_disc_pl = (void *)payload_in;
>      struct media_op_discovery_out_pl *media_out_pl =
>          (struct media_op_discovery_out_pl *)payload_out;
> +    int total = ARRAY_SIZE(media_op_matrix);
>      int num_ops, start_index, i;
>      int count = 0;
>  
> @@ -2609,24 +2610,20 @@ static CXLRetCode media_operations_discovery(uint8_t *payload_in,
>       * sub class command.
>       */
>      if (media_op_in_disc_pl->dpa_range_count ||
> -        start_index + num_ops > ARRAY_SIZE(media_op_matrix)) {
> +        start_index >= total) {
>          return CXL_MBOX_INVALID_INPUT;
>      }
>  
>      media_out_pl->dpa_range_granularity = CXL_CACHE_LINE_SIZE;
> -    media_out_pl->total_supported_operations =
> -                                     ARRAY_SIZE(media_op_matrix);
> -    if (num_ops > 0) {
> -        for (i = start_index; i < start_index + num_ops; i++) {
> -            media_out_pl->entry[count].media_op_class =
> -                    media_op_matrix[i].media_op_class;
> -            media_out_pl->entry[count].media_op_subclass =
> -                        media_op_matrix[i].media_op_subclass;
> -            count++;
> -            if (count == num_ops) {
> -                break;
> -            }
> -        }
> +    media_out_pl->total_supported_operations = total;
> +
> +    num_ops = MIN(num_ops, total - start_index);
> +    for (i = 0; i < num_ops; i++) {
> +        media_out_pl->entry[count].media_op_class =
> +                media_op_matrix[start_index + i].media_op_class;
> +        media_out_pl->entry[count].media_op_subclass =
> +                    media_op_matrix[start_index + i].media_op_subclass;
Patch in general looks good, but the indenting here is a bit too creative
/ inconsistent.
        media_out_pl->entry[count].media_op_class =
                media_op_matrix[start_index + i].media_op_class;
        media_out_pl->entry[count].media_op_subclass =
                media_op_matrix[start_index + i].media_op_subclass;

or something along those lines.

> +        count++;
>      }
>  
>      media_out_pl->num_of_supported_operations = count;