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    SubjectRe: [PATCH 3/3] add support for DWC UFS Host Controller
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    Hi Mark and Arnd,

    I am planning the v2 of this patch set. I have a doubt in the version
    compatibility strings... The core driver must support the UFS 2.0 controller and
    this patch set includes a patch that adds 2.0 capabilities to it. The core
    driver can get from the controller's version and with that use or not a specific
    2.0 feature.

    What would be the real added-value of having a compatibility string like
    "snps,ufshcd-1.1" and "snps,ufshcd-2.0" if the driver can perform as 2.0 if it
    detects a 2.0 controller? Are you saying that a user that puts "snps,ufshcd-1.1"
    in the DT compatibility string disables the UFS 2.0 in the core driver despite
    the controller is 2.0? Please clarify.

    Thanks,
    Joao

    On 2/4/2016 4:27 PM, Mark Rutland wrote:
    > On Wed, Feb 03, 2016 at 03:54:48PM +0000, Joao Pinto wrote:
    >> Hi,
    >>
    >> On 2/3/2016 3:39 PM, Arnd Bergmann wrote:
    >>> On Wednesday 03 February 2016 15:01:34 Joao Pinto wrote:
    >>>>
    >>>> Hi Arnd,
    >>>>
    >>>> On 2/3/2016 12:54 PM, Arnd Bergmann wrote:
    >>>>> On Wednesday 03 February 2016 11:28:26 Joao Pinto wrote:
    >>>>>>
    >>>>>> Signed-off-by: Joao Pinto <jpinto@synopsys.com>
    >>>>>
    >>>>> This needs a changelog comment, like every patch.
    >>>>>
    >>>>>> @@ -0,0 +1,16 @@
    >>>>>> +* Universal Flash Storage (UFS) DesignWare Host Controller
    >>>>>> +
    >>>>>> +DWC_UFSHC nodes are defined to describe on-chip UFS host controllers.
    >>>>>> +Each UFS controller instance should have its own node.
    >>>>>> +
    >>>>>> +Required properties:
    >>>>>> +- compatible : compatible list, contains "snps,ufshcd"
    >>>>>
    >>>>> Are there multiple versions of this controller? Usually for designware
    >>>>> parts the version is known, so we should document which versions exist
    >>>>
    >>>> This controller recent releases was 2.0, but we released last year 1.1. The
    >>>> driver works with both. The driver must work with all DWC UFS versions.
    >>>
    >>> Ok, then make the driver match on the "snps,ufshcd-1.1" compatible
    >>> string, but document both strings in the binding document, and make
    >>> it mandatory to specify the 1.1 version as a compatible fallback.
    >>>
    >>> If we ever need to handle a quirk for the 2.0 version then, it can
    >>> easily be done.
    >>
    >> We need the driver to support UFS 2.0 because it is our latest release and is
    >> the done that Synopsys is focused now. We could call it "snps, ufshcd-2.0" then.
    >> What do you think?
    >
    > Arnd's point was that the driver can handle only "snps,ufshcd-1.1" for
    > now, and in your DT you can have:
    >
    > compatible = "snps,ufshcd-2.0", "snps,ufshcd-1.1";
    >
    > That allows driver to handle 2.0 and 1.1 without knowing anything about
    > 2.0 for now. If in future the two need to be handled differently we can
    > update the driver to explicitly match "snps,ufshcd-2.0".
    >
    > Regardless, both compatible string should go in the documentation, and
    > it should be explicitly mentioned that "snps,ufshcd-1.1" should be used
    > as a fallback entry.
    >
    > Mark.
    >

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