Re: [PATCH] nvme: clear the prp2 field of the nvme command.

["Rao, Lei" <lei.rao@intel.com>]

On 11/29/2022 12:16 PM, Chaitanya Kulkarni wrote:
> On 11/28/22 17:47, Lei Rao wrote:
>> If the prp2 field is not filled in nvme_setup_prp_simple(), the prp2
>> field is garbage data. According to nvme spec, the prp2 is reserved if
>> the data transfer does not cross a memory page boundary. Writing a
>> reserved coded value into a controller property field produces undefined
>> results, so it needs to be cleared in nvme_setup_rw().
>>
>> Signed-off-by: Lei Rao <lei.rao@intel.com>
> 
> if it is reserved then controller shoule ignore this field, no ?

It's feasible for the controller to ignore this field. But our controller has
stricter checks, and if prp2 is not used but has a value, some warnings will be
printed. According to the NVMe spec, it seems to write a reserved field produces
an undefined result, so maybe clearing it is better.

Thanks,
Lei

> 
> not sure if original author wanted to avoid an extra assignment
> in the fast path with assumption that reserved fields should be
> ignored if it is then we should avoid this, if not then looks good
> 
> Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
> 
> -ck
>