Re: [PATCH v2 01/16] nvme: fix pci doorbell size calculation

[Philippe Mathieu-Daudé]

On 4/15/20 3:01 PM, Klaus Jensen wrote:
> From: Klaus Jensen <address@hidden>
>
> The size of the BAR is 0x1000 (main registers) + 8 bytes for each
> queue. Currently, the size of the BAR is calculated like so:
>
>      n->reg_size = pow2ceil(0x1004 + 2 * (n->num_queues + 1) * 4);
>
> Since the 'num_queues' parameter already accounts for the admin queue,
> this should in any case not need to be incremented by one. Also, the
> size should be initialized to (0x1000).
>
>      n->reg_size = pow2ceil(0x1000 + 2 * n->num_queues * 4);
>
> This, with the default value of num_queues (64), we will set aside room
> for 1 admin queue and 63 I/O queues (4 bytes per doorbell, 2 doorbells
> per queue).
>
> Signed-off-by: Klaus Jensen <address@hidden>
> Reviewed-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>   hw/block/nvme.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> index d28335cbf377..5b5f75c9d29e 100644
> --- a/hw/block/nvme.c
> +++ b/hw/block/nvme.c
> @@ -43,6 +43,9 @@
>   #include "trace.h"
>   #include "nvme.h"
>   
> +#define NVME_REG_SIZE 0x1000
> +#define NVME_DB_SIZE  4
> +
>   #define NVME_GUEST_ERR(trace, fmt, ...) \
>       do { \
>           (trace_##trace)(__VA_ARGS__); \
> @@ -1345,7 +1348,9 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
>       pcie_endpoint_cap_init(pci_dev, 0x80);
>   
>       n->num_namespaces = 1;
> -    n->reg_size = pow2ceil(0x1004 + 2 * (n->num_queues + 1) * 4);
> +
> +    /* num_queues is really number of pairs, so each has two doorbells */
> +    n->reg_size = pow2ceil(NVME_REG_SIZE + 2 * n->num_queues * NVME_DB_SIZE);

Unrelated to this change, but it would be cleaner to initialize reg_size 
using MAX_NUM_QUEUES, then in the I/O handler log GUEST_ERROR when 
registers > n->num_queues accessed. This would model closer to the hardware.

>       n->ns_size = bs_size / (uint64_t)n->num_namespaces;
>   
>       n->namespaces = g_new0(NvmeNamespace, n->num_namespaces);