Re: [PATCH v2 2/3] PCI/NPEM: Add Native PCIe Enclosure Management support

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

Hi,
Thanks for feedback Dan!

On Wed, 29 May 2024 11:38:12 +0200
Lukas Wunner <lukas@wunner.de> wrote:

> On Tue, May 28, 2024 at 10:21:10PM -0700, Dan Williams wrote:
> > Mariusz Tkaczyk wrote:  
> > > +config PCI_NPEM
> > > +	bool "Native PCIe Enclosure Management"
> > > +	depends on LEDS_CLASS=y  
> > 
> > I would have expected
> > 
> >     depends on NEW_LEDS
> >     select LEDS_CLASS  
> 
> Hm, a quick "git grep -C 2 'depends on NEW_LEDS'" shows that noone else
> does that.  Everyone else either selects both NEW_LEDS and LEDS_CLASS
> or depends on both or depends on just LEDS_CLASS.
> 
> (Since LEDS_CLASS is constrained to "if NEW_LEDS", depending on both
> seems pointless, so I'm not sure why some people do that.)
> 
> I guess it would be good to get guidance from leds maintainers what
> the preferred modus operandi is.

Pavel, could you please advice?
I have no clue which way I should take so I prefer to keep current approach.

> 
> 
> > > +#define for_each_indication(ind, inds) \
> > > +	for (ind = inds; ind->bit; ind++)
> > > +
> > > +/* To avoid confusion, do not keep any special bits in indications */  
> > 
> > I am confused by this comment. What "special bits" is this referring to?  
> 
> I think it's referring to bit 0 in the Status and Control register,
> which is a master "NPEM Capable" and "NPEM Enable" bit.

Yes, there are 2 special bits for capability/control
NPEM_CAP_CAPABLE/NPEM_ENABLE and NPEM_CAP_RESET/NPEM_RESET.

I wanted to highlight that these bits are not included in the cache. I will try
to make it more precise in v3.

> 
> 
> > > +struct npem_ops {
> > > +	const struct indication *inds;  
> > 
> > @inds is not an operation, it feels like something that belongs as
> > another member in 'struct npem'. What drove this data to join 'struct
> > npem_ops'?  
> 
> The native NPEM register interface supports enclosure-specific indications
> which the DSM interface does not support.  So those indications are
> present in the native npem_ops->inds and not present in the DSM
> npem_ops->inds.

Yes, I need to differentiate DSM and NPEM indications. DSM has own indications
list.

> 
> 
> > > --- a/include/uapi/linux/pci_regs.h
> > > +++ b/include/uapi/linux/pci_regs.h  
> [...]
> > > +#define  PCI_NPEM_IND_SPEC_0		0x00800000
> > > +#define  PCI_NPEM_IND_SPEC_1		0x01000000
> > > +#define  PCI_NPEM_IND_SPEC_2		0x02000000
> > > +#define  PCI_NPEM_IND_SPEC_3		0x04000000
> > > +#define  PCI_NPEM_IND_SPEC_4		0x08000000
> > > +#define  PCI_NPEM_IND_SPEC_5		0x10000000
> > > +#define  PCI_NPEM_IND_SPEC_6		0x20000000
> > > +#define  PCI_NPEM_IND_SPEC_7		0x40000000  
> > 
> > Given no other driver needs this, I would define them locally in
> > drivers/pci/npem.c.  
> 
> This is a uapi header, so could be used not just by other drivers
> but by user space.
> 
> It's common to add spec-defined register bits to this header file
> even if they're only used by a single source file in the kernel.
> 

I will stay with current state while waiting for Bjorn's voice here.

I will send v3 with fixes requested by Dan and Ilpo but I still need Stuart
feedback on DSM patch.

Thanks,
Mariusz