Re: [PATCH] spraid: initial commit of Ramaxel spraid driver

[Yanling Song <songyl@ramaxel.com>]

On Wed, 13 Oct 2021 15:00:07 -0700
Bart Van Assche <bvanassche@acm.org> wrote:

> On 10/12/21 11:50 PM, Yanling Song wrote:
> > On Tue, 12 Oct 2021 09:59:30 -0700
> > Bart Van Assche <bvanassche@acm.org> wrote:  
> >> Why is it that SG_IO is not sufficient? This is something that
> >> should have been explained in the patch description.  
> > 
> > There are two cases that there are no SG devices and SG_IO cannot
> > work. 1. To access raid controller:
> > a. Raid controller is a scsi host, not a scsi device, so there
> > is no SG device associated with it.
> > b. Even there is a scsi device for raid controller, SG_IO
> > cannot work when something wrong with IO queue and only admin queue
> > can work;
> > 2. To access the physical disks behinds raid controller:
> > raid controller only reports VDs to OS and only VDs have SG
> > devices. OS has no idea about physical disks behinds raid
> > controller and there is no SG devices associated with physical
> > disks.  
> 
> Please take a look at the bsg_setup_queue() call in ufs_bsg_probe(). 
> That call associates a BSG queue with the UFS host. That queue
> supports requests of type struct ufs_bsg_request. The Fibre Channel
> transport driver does something similar. I believe that this is a
> better solution than introducing entirely new ioctls.

I wish there was a standard way to address the ioctrl issue.
Unfortunately ioctrl is the only way to meet our requirements as listed
in the above.
As discussed in previous megaraid's patchsets:
https://lore.kernel.org/linux-scsi/yq1inc2y019.fsf@oracle.com/, that's
why every raid controller has it's own ioctrl.