scsi: hisi_sas: Allocate DFX memory during dump trigger

scsi: hisi_sas: Allocate DFX memory during dump trigger

Currently, if CONFIG_SCSI_HISI_SAS_DEBUGFS_DEFAULT_ENABLE is enabled, the
memory space used by DFX is allocated during device initialization, which
occupies a large number of memory resources. The memory usage before and
after the driver is loaded is as follows:

Memory usage before the driver is loaded:
$ free -m
         total        used        free      shared  buff/cache   available
Mem:     867352        2578      864037          11         735  861681
Swap:    4095           0        4095

Memory usage after the driver which include 4 HBAs is loaded:
$ insmod hisi_sas_v3_hw.ko
$ free -m
         total        used        free      shared  buff/cache	available
Mem:     867352        4760      861848          11	  743   859495
Swap:    4095           0        4095

The driver with 4 HBAs connected will allocate about 110 MB of memory
without enabling debugfs.

Therefore, to avoid wasting memory resources, DFX memory is allocated
during dump triggering. The dump may fail due to memory allocation
failure. After this change, each dump costs about 10 MB of memory, and each
dump lasts about 100 ms.

Signed-off-by: Yihang Li <liyihang9@huawei.com>
Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Link: https://lore.kernel.org/r/1694571327-78697-4-git-send-email-chenxiang66@hisilicon.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>