Re: [PATCH v3 2/4] dt-bindings: nvmem: Add properties needed for blowing fuses

[Doug Anderson <dianders@chromium.org>]

Hi,

On Thu, Jun 18, 2020 at 3:10 AM Srinivas Kandagatla
<srinivas.kandagatla@linaro.org> wrote:
>
> +Adding SBoyd.
>
> On 17/06/2020 18:22, Doug Anderson wrote:
> > Hi,
> >
> > On Wed, Jun 17, 2020 at 8:19 AM Srinivas Kandagatla
> > <srinivas.kandagatla@linaro.org> wrote:
> >>
> >>
> >>
> >> On 17/06/2020 15:51, Douglas Anderson wrote:
> >>> From: Ravi Kumar Bokka <rbokka@codeaurora.org>
> >>>
> >>> On some systems it's possible to actually blow the fuses in the qfprom
> >>> from the kernel.  Add properties to support that.
> >>>
> >>> NOTE: Whether this is possible depends on the BIOS settings and
> >>> whether the kernel has permissions here, so not all boards will be
> >>> able to blow fuses in the kernel.
> >>>
> >>> Signed-off-by: Ravi Kumar Bokka <rbokka@codeaurora.org>
> >>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> >>> ---
> >>>
> >>> Changes in v3:
> >>> - Add an extra reg range (at 0x6000 offset for SoCs checked)
> >>> - Define two options for reg: 1 item or 4 items.
> >>> - No reg-names.
> >>> - Add "clocks" and "clock-names" to list of properties.
> >>> - Clock is now "sec", not "secclk".
> >>> - Add "vcc-supply" to list of properties.
> >>> - Fixed up example.
> >>>
> >>>    .../bindings/nvmem/qcom,qfprom.yaml           | 45 ++++++++++++++++++-
> >>>    1 file changed, 43 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/nvmem/qcom,qfprom.yaml b/Documentation/devicetree/bindings/nvmem/qcom,qfprom.yaml
> >>> index 5efa5e7c4d81..b195212c6193 100644
> >>> --- a/Documentation/devicetree/bindings/nvmem/qcom,qfprom.yaml
> >>> +++ b/Documentation/devicetree/bindings/nvmem/qcom,qfprom.yaml
> >>> @@ -17,8 +17,27 @@ properties:
> >>>        const: qcom,qfprom
> >>>
> >>>      reg:
> >>> -    items:
> >>> -      - description: The corrected region.
> >>> +    # If the QFPROM is read-only OS image then only the corrected region
> >>> +    # needs to be provided.  If the QFPROM is writable then all 4 regions
> >>> +    # must be provided.
> >>> +    oneOf:
> >>> +      - items:
> >>> +          - description: The corrected region.
> >>> +      - items:
> >>> +          - description: The corrected region.
> >>> +          - description: The raw region.
> >>> +          - description: The config region.
> >>> +          - description: The security control region.
> >>> +
> >>> +  # Clock must be provided if QFPROM is writable from the OS image.
> >>> +  clocks:
> >>> +    maxItems: 1
> >>
> >>
> >>> +  clock-names:
> >>> +    const: sec
> >>
> >> Do we need clock-names for just one clock here?
> >
> > I think technically you can get by without, but convention is that
> > clock-names are always provided for clocks.  It's talked about in the
> > same link I sent that talked about reg-names:
> >
> > https://lore.kernel.org/r/CAL_Jsq+MMunmVWqeW9v2RyzsMKP+=kMzeTHNMG4JDHM7Fy0HBg@mail.gmail.com/
> >
>
> TBH, This is total confusion!!!
>
> when to use "*-names" Device tree bindings is totally depended on Linux
> Subsystem interfaces!
>
> And what is the starting point to draw this line?

Definitely confusing and mostly because the dts stuff grew organically
for a while there.  It does feel like Rob is pretty clear on the
current state of things and the policy in the link I provided, though.


> > Specifically, Rob said:
> >
> >> That probably is because the clock binding has had clock-names from
> >> the start (it may have been the first one). That was probably partly
> >> due to the clock API also was mainly by name already if we want to
> >> admit Linux influence on bindings
> >
> > Basically the standard way for getting clocks in Linux is
> > clk_get(name).  With just one clock you can call clk_get(NULL) and I
> > believe that works, but when you add the 2nd clock then you have to
> > switch APIs to one of the less-commonly-used variants.
>
> In previous NON-DT life clk_get api name argument comes from the clk
> names that clk provider registered the clocks with.
>
> If I remember this correctly, the name that is refereed here for
> clk_get() is old clkdev api based on clk_lookups and is not the same as
> clk-names that we have in Device tree. Atleast in this case!
>
> clk-names has two objectives in DT:
> 1> To find the index of the clock in the clocks DT property.
>
> 2> If actual clk name is specified then if "1" fails then name could
> potentially fallback to use old clkdev based clk_lookups.
>
> In this specific case we have "sec" as clock-names which is totally used
> for indexing into clocks property and it can not be used for (2) as
> there is no clk named "sec" registered by any of the clk providers.
>
> So this does not justify the reasoning why "clock-names" should be used
> while "reg-names" should not be used!. Both of them are going to be
> finally used for indexing into there respective properties.

Right, you just have to accept the fact that logic doesn't come into
play here.  For clocks, always use "clk-names" but also always use a
consistent order (which is now more enforced by the schema checker).
For "reg" almost never use "reg-names".


> This also brings in greater confusion for both existing and while adding
> bindings with "*-names" for new interfaces.
>
> Rob, can you please provide some clarity and direction on when to
> use/not-use *-names properties!

If I had to guess Rob will say that we shouldn't add more places where
the convention is to have "-names".


I will put posting v4 of this patch on pause until this is resolved to
avoid fragmenting the discussion.


-Doug