Re: [PATCH v2 1/2] dt-bindings: spi: Qualcomm Quad SPI(QSPI) documentation

Hi,
On Mon, Sep 24, 2018 at 11:23 AM Trent Piepho [off-list ref] wrote:

On Mon, 2018-09-24 at 10:13 -0700, Doug Anderson wrote:

quoted

IIUC previous suggestions about just naming it based on the first SoC
was due to the difficulty of coming up with a good generic name to
give something.  For instance you definitely wouldn't want to name it
"qcom-qspi-sdm8xx" because you have no idea what future SoCs will be
numbered.

And the hypothetical sdm899 might use a non-compatible device that uses
a different driver, and that really makes "qcom-qspi-sdm8xx" look dumb.

quoted

In the case here calling it "qcom,qspi-v1" is better than that and if
Rob gives the thumbs up then I won't object to it.  In general though
looking at other device tree bindings this doesn't seem like a thing
commonly done.  Perhaps if we decide it's useful here we should start
suggesting it everywhere...

It would help if the programming model or IP core name or whatever this
is using was mentioned in the public reference manual for the SoC.
Then is a lot more clear that a number of different SoCs all have the
same quad spi controller inside them.

Usually it's not like that.  The RMs just say, "it's got a SPI master
with these registers."  What SoCs use the same IP module, which
different?  When did they make a new version?  The silicon vendors
don't tell you this.  So any name we make up for the IP module likely
doesn't match reality.

Note that Rob did recently give a positive review to a similar binding.  See:

https://lore.kernel.org/patchwork/patch/979432/

Specifically the text from that binding was:

+                  Qcom SoCs must contain, as below, SoC-specific compatibles
+                  along with "qcom,smmu-v2":
+                  "qcom,msm8996-smmu-v2", "qcom,smmu-v2",
+                  "qcom,sdm845-smmu-v2", "qcom,smmu-v2".

Given Rob's positive review there, it seems like it would be fine to do:

  "qcom,sdm845-qspi", "qcom,qspi-v1".

NOTE: In our case we don't need the "-v1" in SoC-specific case since
there's only one Quad SPI driver there.  As I understand it the reason
we needed the -v2 in the SoC-specific case for the SMMU was that there
are two totally different SMMUs in SDM845.  You can see history in the
v15 patch <https://lore.kernel.org/patchwork/patch/977888/>


-Doug