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



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