Message-ID: <YNT0HPOJEoJYipyE@yoga>
Date:   Thu, 24 Jun 2021 16:07:40 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
Cc:     Jassi Brar <jassisinghbrar@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Martin Botka <martin.botka@...ainline.org>,
        ~postmarketos/upstreaming@...ts.sr.ht,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        jamipkettunen@...ainline.org, Andy Gross <agross@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 3/3] mailbox: qcom-apcs: Add SM6125 compatible

On Tue 22 Jun 09:36 CDT 2021, AngeloGioacchino Del Regno wrote:

> Il 22/06/21 05:52, Bjorn Andersson ha scritto:
> > On Mon 21 Jun 22:34 CDT 2021, Jassi Brar wrote:
> > 
> > > On Mon, Jun 21, 2021 at 9:27 PM Bjorn Andersson
> > > <bjorn.andersson@...aro.org> wrote:
> > > > 
> > > > On Mon 21 Jun 20:00 CDT 2021, Jassi Brar wrote:
> > > > 
> > > > > On Mon, Jun 21, 2021 at 6:35 PM Bjorn Andersson
> > > > > <bjorn.andersson@...aro.org> wrote:
> > > > > > 
> > > > > > On Mon 21 Jun 18:19 CDT 2021, Rob Herring wrote:
> > > > > > 
> > > > > > > On Mon, Jun 21, 2021 at 5:10 PM Jassi Brar <jassisinghbrar@...il.com> wrote:
> > > > > > > > 
> > > > > > > > On Mon, Jun 21, 2021 at 2:46 PM Rob Herring <robh+dt@...nel.org> wrote:
> > > > > > > > > 
> > > > > > > > > On Sun, Jun 20, 2021 at 10:03 PM Jassi Brar <jassisinghbrar@...il.com> wrote:
> > > > > > > > > > 
> > > > > > > > > > On Sat, Jun 12, 2021 at 4:46 AM Martin Botka
> > > > > > > > > > <martin.botka@...ainline.org> wrote:
> > > > > > > > > > > 
> > > > > > > > > > > This commit adds compatible for the SM6125 SoC
> > > > > > > > > > > 
> > > > > > > > > > > Signed-off-by: Martin Botka <martin.botka@...ainline.org>
> > > > > > > > > > > ---
> > > > > > > > > > > Changes in V2:
> > > > > > > > > > > None
> > > > > > > > > > > Changes in V3:
> > > > > > > > > > > Change compatible to apcs-hmss-global
> > > > > > > > > > >   drivers/mailbox/qcom-apcs-ipc-mailbox.c | 5 +++++
> > > > > > > > > > >   1 file changed, 5 insertions(+)
> > > > > > > > > > > 
> > > > > > > > > > > diff --git a/drivers/mailbox/qcom-apcs-ipc-mailbox.c b/drivers/mailbox/qcom-apcs-ipc-mailbox.c
> > > > > > > > > > > index f25324d03842..f24c5ad8d658 100644
> > > > > > > > > > > --- a/drivers/mailbox/qcom-apcs-ipc-mailbox.c
> > > > > > > > > > > +++ b/drivers/mailbox/qcom-apcs-ipc-mailbox.c
> > > > > > > > > > > @@ -57,6 +57,10 @@ static const struct qcom_apcs_ipc_data sdm660_apcs_data = {
> > > > > > > > > > >          .offset = 8, .clk_name = NULL
> > > > > > > > > > >   };
> > > > > > > > > > > 
> > > > > > > > > > > +static const struct qcom_apcs_ipc_data sm6125_apcs_data = {
> > > > > > > > > > > +       .offset = 8, .clk_name = NULL
> > > > > > > > > > > +};
> > > > > > > > > > > +
> > > > > > > > > > >   static const struct qcom_apcs_ipc_data apps_shared_apcs_data = {
> > > > > > > > > > >          .offset = 12, .clk_name = NULL
> > > > > > > > > > >   };
> > > > > > > > > > > @@ -166,6 +170,7 @@ static const struct of_device_id qcom_apcs_ipc_of_match[] = {
> > > > > > > > > > >          { .compatible = "qcom,sc8180x-apss-shared", .data = &apps_shared_apcs_data },
> > > > > > > > > > >          { .compatible = "qcom,sdm660-apcs-hmss-global", .data = &sdm660_apcs_data },
> > > > > > > > > > >          { .compatible = "qcom,sdm845-apss-shared", .data = &apps_shared_apcs_data },
> > > > > > > > > > > +       { .compatible = "qcom,sm6125-apcs-hmss-global", .data = &sm6125_apcs_data },
> > > > > > > > > > >          { .compatible = "qcom,sm8150-apss-shared", .data = &apps_shared_apcs_data },
> > > > > > > > > > >          { .compatible = "qcom,sdx55-apcs-gcc", .data = &sdx55_apcs_data },
> > > > > > > > > > >          {}
> > > > > > > > > > > 
> > > > > > > > > > These all are basically different names for the same controller.
> > > > > > > > > > The 'offset' is a configuration parameter and the 'clock', when NULL,
> > > > > > > > > > is basically some "always-on" clock.
> > > > > > > > > > I am sure we wouldn't be doing it, if the controller was third-party.
> > > > > > > > > 
> > > > > > > > > If newer implementations are 'the same', then they should have a
> > > > > > > > > fallback compatible to the existing one that is the same and no driver
> > > > > > > > > change is needed. If the differences are board or instance (within an
> > > > > > > > > SoC) specific, then a DT property would be appropriate.
> > > > > > > > > 
> > > > > > > > The controllers (13 now) only differ by the 'offset' where the
> > > > > > > > registers are mapped. Clock-name is a pure s/w artifact.
> > > > > > > > So, maybe we could push all these in DT.
> > > > > > > 
> > > > > > > Why is 'reg' not used for the offset?
> > > > > > > 
> > > > > > 
> > > > > > The DT node and its "reg" describes the whole IP block.
> > > > > > 
> > > > > > The particular register that we care of has, as you can see, moved
> > > > > > around during the various platforms and some incarnations of this IP
> > > > > > block provides controls for CPU-related clocks as well.
> > > > > > 
> > > > > > We can certainly have the multiple compatible points to the same
> > > > > > apcs_data, but I'm not able to spot a reasonable "catch-all compatible"
> > > > > > given that I don't see any natural groupings.
> > > > > > 
> > > > > Any platform that comes later may reuse the already available compatible.
> > > > > For example drop this patch and reuse "qcom,sdm660-apcs-hmss-global" ?
> > > > > 
> > > > 
> > > > The problem is that this would change the meaning of
> > > > "qcom,sdm660-apcs-hmss-global" from meaning "The apcs hmss global block
> > > > _in_ sdm660" to "any random apcs block with the mailbox register at
> > > > offset 8".
> > > > 
> > > To me, the deeper problem seems to be naming a controller "The apcs
> > > hmss global block _in_ sdm660" just because the h/w manual hasn't
> > > given a name to it.  But that is okay too, if we name the subsequent
> > > controllers as "the same as one in sdm660" and provide the h/w
> > > configuration 'offset' via a DT property.
> > > 
> > 
> > As I said, I'd need to dig through the hardware documentation for the
> > various platforms to see if I can find what the common denominators are.
> > We've always seen this as "the apcs hmss global block _in_ <platform>".
> > 
> > > > > > > In any case, we can't really get rid of the first 13 instances though...
> > > > > > > 
> > > > > > 
> > > > > > Right, we have the problem that we have DTBs out there that relies on
> > > > > > these compatibles, but as Jassi requests we'd have to start describing
> > > > > > the internal register layout in DT - which this binding purposefully
> > > > > > avoids.
> > > > > > 
> > > > > Not these strings, but 'offset' and 'clock-name' as optional
> > > > > properties that new platforms can use.
> > > > > 
> > > > 
> > > > Relying on completely generic compatibles to match the driver and then
> > > > distinguish each platform using additional properties is exactly what
> > > > Qualcomm does downstream.  The community has clarified countless times
> > > > that this is not the way to write DT bindings.
> > > > 
> > > Yes, and I don't suggest it otherwise. For h/w quirks and
> > > extra/missing features, it does make sense to have different
> > > compatibles.
> > > 
> > 
> > But what you're suggesting assumes that they are the same and that we're
> > done implementing all the software for this block. The platform specific
> > compatible allows us to postpone that question.
> > 
> > > However, for _trivial_ variations let us get that value from DT.
> > > 'offset' is anyway a h/w property.
> > > That way we won't be distinguishing platforms using dt properties, but
> > > only support different platforms seamlessly.
> > > 
> > 
> > As I said previously, this goes against the direction provided by the DT
> > maintainers. If a property is platform specific this should be expressed
> > by the compatible.
> > 
> > > On second thought, we have grown from 2 to 13 aliases in 4 yrs. I only
> > > have to ignore 3 times/annum to lead a peaceful life ;)
> > > 
> > 
> > True, but I'll try to find some time to see if we have some reuse of the
> > IP block to allow us to use some generic compatible.
> > 
> > We'd still need a patch in the DT binding for every single platform, but
> > we should be able to avoid the compatible additions in the driver.
> > 
> 
> Hello Jassi, Bjorn
> 
> I've read the entire thread and I can't say that Jassi is entirely wrong
> but I also agree with Bjorn on this matter.
> 
> This driver is here to "simply" manage the register offset in the APCS
> IP, which is a pretty straightforward operation.
> If you check in this driver, you will see that there's not much
> duplication between the various qcom_apcs_ipc_data that we have for
> all the different SoCs.
> 
> Checking further, we can effectively reduce the amount of compatibles
> in this driver by simply removing some "duplicated" instances and in
> particular:
> ipq6018, ipq8074, msm8916, msm8994, msm8998, sdm660
> 
> and eventually replacing them with either of:
> - 8bits_apcs_data    qcom,apcs-apps-global-8bit
>                      qcom,apcs-kpss-global-8bit

I don't like those compatibles, simply because the binding is supposed
to describe the hardware block, not the fact that Linux _currently_ only
pokes this one register.

We could probably "qcom,apss-global" as a catch-all for at least sc7180,
sc7280, sdm845, sm8150, sm8250 and sm8350.

But look at 8996 and 8998, both named "something-hmss-something", with
different register layout. And a quick glance seems to indicate that
sdm660 isn't a hmss after all :/

But introducing qcom,apss-global should catch a bunch of the newer
platforms.


On the DT binding side we still need the platform-specific ones and we
need each one to be added to the binding regardless of the catch-all in
the driver.

Regards,
Bjorn

> - more_appropriate_name_apcs_data qcom,(...blah)
> 
> This would mean that we would have to use a generic "qcom,apcs-clk" as
> the clk_name, but no other modifications would be done, apart checking
> the return value to choose whether to print or not the dev_err when the
> clock name is specified but not present in dt, since the driver is
> already actually covering this case.
> 
> That would make us able to reduce the compatibles from 6 to 2, relative
> to the aforementioned SoC specific bindings.
> I'm positive that, through time, when new SoCs arrive, we would avoid
> getting this compatible list to be megabytes long...
> 
> Right now it's not an issue, but since Qualcomm SoCs are now being very
> actively upstreamed, I can see this coming in the future, somehow.
> 
> 
> Of course this means that we're getting some fair amount of patch-noise
> in the mailing lists, since all qcom dtsi files will have to be changed,
> but that shouldn't really be a problem, I guess.
> 
> I'm sure that I'm not the only one with such a "wow-idea" in mind :)
> 
> Yours,
> - Angelo
> 
> > Regards,
> > Bjorn
> > 
> 

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