[PATCH 18/18] nvme: move chardev and sysfs interface to common code

[J Freyensee]

On Thu, 2015-10-22 at 09:45 +0200, Christoph Hellwig wrote:
> On Wed, Oct 21, 2015 at 05:11:11PM -0700, J Freyensee wrote:
> > > +	spin_lock(&dev_list_lock);
> > > +	list_for_each_entry(ctrl, &nvme_ctrl_list, node) {
> > 
> > list_for_each_entry_safe() and/or some type of lock access?
> 
> list_for_each_entry_safe does not synchronize, it just ensures you
> can continue to iterate after deleting the current item.
> 
> And the spin_lock() call above provides the required synchronization.
> 
> > > +	if (result < 0)
> > > +		goto unregister_blkdev;
> > > +	else if (result > 0)
> > > +		nvme_char_major = result;
> > > +
> > > +	nvme_class = class_create(THIS_MODULE, "nvme");
> > 
> > It would be better to have "nvme" as a #define somewhere, probably 
> > in
> > the .h?
> 
> Why?

Well, for starters, it's good practice to have strings like this in a
#define.

I can send a patch to redefine this and 0x4E564D65 in the nvme.h.

> 
> > >  	char name[12];
> > >  	char serial[20];
> > > @@ -60,6 +59,8 @@ struct nvme_ctrl {
> > >  	u16 abort_limit;
> > >  	u8 event_limit;
> > >  	u8 vwc;
> > > +	u32 vs;
> > > +	bool subsystem;
> > 
> > OK, so 'bool subsystem' got added back in.  Not sure still how a 
> > bool
> > helps define a controller into a given subsystem.  Isn't the 
> > definition
> > of an NVM subsystem 1 or more controllers?  So every new 'struct
> > nvme_ctrl' instance is going to set this to 'true'?
> 
> In NVMe 1.0 the concept of subsystems didn't exist.  Now strictly 
> speaking
> what we care about here is if a subsystem _reset_ is supported, but 
> I've
> kept the name from the existing code for now.

OK understood.

> 
> > Or looking into the future, say if this is on a future fabric
> > connection, there could be lots of controllers under lots of 
> > distinct
> > subsystems.  Then I don't know how 'bool subsystem' makes sense and
> > distinguishes a controller in a given NVM subsystem.
> 
> That's not what the flag is used for.  It just indicates if we can do
> a subsystem reset.
> 
> > > @@ -87,7 +88,9 @@ struct nvme_ns {
> > >  struct nvme_ctrl_ops {
> > >  	int (*reg_read32)(struct nvme_ctrl *ctrl, u32 off, u32 
> > > *val);
> > >  	int (*reg_read64)(struct nvme_ctrl *ctrl, u32 off, u64 
> > > *val);
> > > +	int (*reg_write32)(struct nvme_ctrl *ctrl, u32 off, u32 
> > > val);
> > 
> > I don't think they are being used currently, but the ACQ and ASQ 8
> > -byte
> > registers do have RW fields.  Maybe add "int (*reg_write64)()" as 
> > well?
> 
> We can do that once we actually need it.  But at least ACQ and ASQ 
> are
> deeply tied to PCI specific initialization so right now there is no 
> need
> for that.
> 
> > >  	bool (*io_incapable)(struct nvme_ctrl *ctrl);
> > > +	int (*reset_ctrl)(struct nvme_ctrl *ctrl);
> > 
> > Probably would want a "(*shutdown_ctrl)()" as well?
> 
> We currently don't shut the controller down from generic code, so 
> until
> we have a state machine that might do that there's no need for that.
> 
> > 
> > > +	return ctrl->ops->reg_write32(ctrl, NVME_REG_NSSR, 
> > > 0x4E564D65);
> > 
> > It would be really good to have the hex value in a #define, most 
> > likely
> > located in the nvme.h file.
> 
> Feel free to send incremental patches for these sorts of cleanups!