Re: [PATCH v3 09/20] nvme-pci: check DMA ops when indicating support for PCI P2PDMA

[Logan Gunthorpe]

On 2021-09-29 11:06 p.m., Chaitanya Kulkarni wrote:
> Logan,
> 
>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>> index 7efb31b87f37..916750a54f60 100644
>> --- a/drivers/nvme/host/core.c
>> +++ b/drivers/nvme/host/core.c
>> @@ -3771,7 +3771,8 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid,
>>                  blk_queue_flag_set(QUEUE_FLAG_STABLE_WRITES, ns->queue);
>>
>>          blk_queue_flag_set(QUEUE_FLAG_NONROT, ns->queue);
>> -       if (ctrl->ops->flags & NVME_F_PCI_P2PDMA)
>> +       if (ctrl->ops->supports_pci_p2pdma &&
>> +           ctrl->ops->supports_pci_p2pdma(ctrl))
>>                  blk_queue_flag_set(QUEUE_FLAG_PCI_P2PDMA, ns->queue);
>>
>>          ns->ctrl = ctrl;
>> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
>> index 9871c0c9374c..fb9bfc52a6d7 100644
>> --- a/drivers/nvme/host/nvme.h
>> +++ b/drivers/nvme/host/nvme.h
>> @@ -477,7 +477,6 @@ struct nvme_ctrl_ops {
>>          unsigned int flags;
>>   #define NVME_F_FABRICS                 (1 << 0)
>>   #define NVME_F_METADATA_SUPPORTED      (1 << 1)
>> -#define NVME_F_PCI_P2PDMA              (1 << 2)
>>          int (*reg_read32)(struct nvme_ctrl *ctrl, u32 off, u32 *val);
>>          int (*reg_write32)(struct nvme_ctrl *ctrl, u32 off, u32 val);
>>          int (*reg_read64)(struct nvme_ctrl *ctrl, u32 off, u64 *val);
>> @@ -485,6 +484,7 @@ struct nvme_ctrl_ops {
>>          void (*submit_async_event)(struct nvme_ctrl *ctrl);
>>          void (*delete_ctrl)(struct nvme_ctrl *ctrl);
>>          int (*get_address)(struct nvme_ctrl *ctrl, char *buf, int size);
>> +       bool (*supports_pci_p2pdma)(struct nvme_ctrl *ctrl);
>>   };
>>
> 
> Is this new ops only needed for the PCIe transport ? or do you have 
> following patches to use this op for the other transports ?

No, I don't think this will make sense for transports that are not based
on PCI devices.

> If it is only needed for the PCIe then we need to find a way to
> not add this somehow...

I don't see how we can do that. The core code needs to know whether the
transport supports this and must have an operation to query it.

Logan