[PATCHv2] arm64: dts: ti: k3-j721e-beagleboneai64: Enable ACSPCIE output for PCIe1

[Siddharth Vadapalli]

On Mon, Dec 02, 2024 at 12:07:17PM +0100, Krzysztof Kozlowski wrote:

Hello Krzysztof,

> On 02/12/2024 11:58, Siddharth Vadapalli wrote:
> > On Mon, Dec 02, 2024 at 11:14:46AM +0100, Krzysztof Kozlowski wrote:
> > 
> > Hello Krzysztof,
> > 
> >> On 02/12/2024 11:11, Romain Naour wrote:
> >>> From: Romain Naour <romain.naour at skf.com>
> >>>
> >>> Unlike the SK-TDA4VM (k3-j721e-sk) board, there is no clock generator
> >>> (CDCI6214RGET) on the BeagleBone AI-64 (k3-j721e-beagleboneai64) to
> >>> provide PCIe refclk signal to PCIe Endponts. So the ACSPCIE module must
> >>> provide refclk through PCIe_REFCLK pins.
> >>>
> >>> Use the new "ti,syscon-acspcie-proxy-ctrl" property to enable ACSPCIE
> >>> module's PAD IO Buffers.
> >>>
> >>> Reuse the compatible "ti,j784s4-acspcie-proxy-ctrl" since the ACSPCIE
> >>> buffer and its functionality is the same across all K3 SoCs.
> >>>
> >>> Cc: Siddharth Vadapalli <s-vadapalli at ti.com>
> >>> Signed-off-by: Romain Naour <romain.naour at skf.com>
> >>> ---
> >>> With this patch, we can remove "HACK: Sierra: Drive clock out" patch
> >>> applied on vendor kernel for BeagleBone AI-64:
> >>> https://openbeagle.org/beagleboard/linux/-/commit/ad65d7ef675966cdbc5d75f2bd545fad1914ba9b
> >>>
> >>> v2:
> >>>  - use generic style comments
> >>>  - use "syscon" as generic node name for "acspcie0_proxy_ctrl" node
> >>>  - Keep the compatible "ti,j784s4-acspcie-proxy-ctrl" since the
> >>>    ACSPCIE buffer and its functionality is the same across all K3 SoCs.
> >>>    (Siddharth Vadapalli)
> >>>
> >>>    "The compatible "ti,j784s4-acspcie-pcie-ctrl" should be reused for
> >>>    J721E and all other K3 SoCs.
> >>
> >> No, it shouldn't and you got comment on this. You always need specific
> >> compatible, see writing bindings doc.
> > 
> > Could you please clarify in which cases reusing the compatible is
> > permissible? The list of compatibles at:
> 
> Never? You always need specific compatible. Did you read the writing
> bindings document?

I went through the bindings document again at:
https://www.kernel.org/doc/Documentation/devicetree/bindings/writing-bindings.rst
It mentions:
- DON'T use 'syscon' alone without a specific compatible string. A 'syscon'
  hardware block should have a compatible string unique enough to infer the
  register layout of the entire block (at a minimum).

The ACSCPCIE Block as well as its integration across all of TI's K3 SoCs
is the same i.e. same Hardware/IP. The register bits corresponding to
the feature to be enabled/disabled via the ACSPCIE block are the same as
well i.e. "register layout can be inferred". The same goes for the
compatibles listed below in my previous reply i.e. they aren't bugs.
Same IP and integration across SoCs and hence reused in the sense of
Hardware and not Software. I hope this clarifies the rationale for the
"reuse".

> 
> > https://github.com/torvalds/linux/blob/v6.12/Documentation/devicetree/bindings/mfd/syscon.yaml#L112
> > namely,
> >           - ti,am62-opp-efuse-table
> >           - ti,am62-usb-phy-ctrl
> >           - ti,am625-dss-oldi-io-ctrl
> >           - ti,am62p-cpsw-mac-efuse
> >           - ti,am654-dss-oldi-io-ctrl
> >           - ti,j784s4-pcie-ctrl
> > have all been reused for different TI SoCs since they all correspond to the
> > device functionality enabled via the CTRL_MMR System Controller registers.
> 
> If you find a bug, does it mean you can send new patch introducing the
> same bug?

[...]

Regards,
Siddharth.