Re: [RFC PATCH 3/9] of: mtd: add NAND timings retrieval support

[boris brezillon]

On 08/01/2014 20:13, Jason Gunthorpe wrote:
> On Wed, Jan 08, 2014 at 08:00:02PM +0100, boris brezillon wrote:
> > Hello Jason,
> >
> > Le 08/01/2014 19:34, Jason Gunthorpe a ?crit :
> > > On Wed, Jan 08, 2014 at 03:21:58PM +0100, Boris BREZILLON wrote:
> > >
> > > > +int of_get_nand_timings(struct device_node *np, struct nand_timings *timings)
> > > > +{
> > > > +	memset(timings, 0, sizeof(*timings));
> > > > +	of_property_read_u32(np, "tCLS-min", &timings->tCLS_min);
> > > > +	of_property_read_u32(np, "tCLH-min", &timings->tCLH_min);
> > > > +	of_property_read_u32(np, "tCS-min", &timings->tCS_min);
> > > [..]
> > >
> > > A while ago when discussing another controller it was pointed out
> > > these values are all auto-probable directly from the NAND via a ONFI
> > > defined GET FEATURE @0x01 query, and adding these timings to the DT
> > > was NAK'd..
> > >
> > > Basically you set the interface to the slowest ONFI timing mode, do
> > > the GET FEATURE to the NAND chip and then increase the interface speed
> > > to the highest mutually supported ONFI mode.
> > > Is there some reason you need to encode this in the DT?
> > What if the NAND does not support the ONFI interface (and this is
> > exactly the case for the NAND available on the cubietruck board:
> > H27UCG8T2ATR).
> Sounds like a good reason to me!
>
> You might want to check if you can boil down the DT timings from the
> huge list to just an ONFI mode number..

Sure, but the sunxi driver needs at least 19 of them...

> I'd echo Rob's comments, the property needs to include the units
> in the name, and I strongly recommend picoseconds for these
> values.

Agreed, picosecond is a more future-proof unit.

> Also, you might want to check that the ONFI names for these parameters
> are used, not a vendor specific name to try and avoid confusion.

I'll check it.

Thanks.

Best Regards,

Boris

> Jason

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/