[PATCH 2/3] nvme: introduce max_segments controller attribute

[Max Gurtovoy]

On 8/16/2017 4:29 PM, Sagi Grimberg wrote:
>
>> Each ctrl will limit max_segments according to it's hardware
>> restrictions. Implement the restriction for RDMA transport.
>>
>> Signed-off-by: Max Gurtovoy <maxg at mellanox.com>
>> ---
>>   drivers/nvme/host/core.c |    4 ++--
>>   drivers/nvme/host/nvme.h |    1 +
>>   drivers/nvme/host/rdma.c |    1 +
>>   3 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>> index 8cf37e7..cc0681e 100644
>> --- a/drivers/nvme/host/core.c
>> +++ b/drivers/nvme/host/core.c
>> @@ -1495,8 +1495,8 @@ static void nvme_set_queue_limits(struct
>> nvme_ctrl *ctrl,
>>       bool vwc = false;
>>         if (ctrl->max_hw_sectors) {
>> -        u32 max_segments =
>> -            (ctrl->max_hw_sectors / (ctrl->page_size >> 9)) + 1;
>> +        u32 max_segments = min_not_zero(ctrl->max_segments,
>> +            (ctrl->max_hw_sectors / (ctrl->page_size >> 9)) + 1);
>
> Why is this needed with patches 1,3 applied?
>
> We set the page_size and we set max_hw_sectors accordingly.

We didn't touch the ctrl->page_size. It's always 4k (the target checks it).
This may cause max_segments to be bigger than hw limitation (in PPC for 
example).