On 9/3/2014 10:34 AM, Bjorn Andersson wrote:
On Wed 03 Sep 08:22 PDT 2014, Kumar Gala wrote:
On Sep 3, 2014, at 9:55 AM, Bjorn Andersson <Bjorn.Andersson@xxxxxxxxxxxxxx> wrote:
On Wed 03 Sep 05:49 PDT 2014, Kumar Gala wrote:
On Sep 2, 2014, at 3:04 PM, Bjorn Andersson <Bjorn.Andersson@xxxxxxxxxxxxxx> wrote:
Changes since v2:
- MODULE_DEVICE_TABLE
- Changed prefix to qcom
- Cleaned up includes
- Rely on reg and num-locks to figure out stride, instead of of_match data
I know Jeff prefers this method of computing stride, but I’m not a fan as
there isn’t a reason one could adjust qcom,num-locks in the dt for some
reason and leave regs alone.
All the current platform it's 32 consecutive mutexes with either 4 or 128 byte
stride, so encoding it as data either way works fine. The hardware you're
trying to describe with your dt is the addresses that spans your mutex
registers and how many there are. So from the HW/dts pov I don't see why you
would like to do this.
Then looking in the caf code, there is a limit of max 8 mutexes. So apparently
there is some sort of usecase, I just don't know what or if it's valid from a
dt pov.
I believe not all the mutexes are meant for the cores running linux.
However, I think we just expect linux to play nice and not touch anything it
isn’t using explicitly.
I would expect so too.
Currently, and I expect this to continue, the first 8 mutexes involve
usecases which involve Linux. The remaining implemented locks support
usecases which do not involve the Linux cores. Generally we expect
Linux to play nice, however it is possible to have hardware memory
protection units in the SoC configured to prevent the Linux cores from
accessing those upper locks. From the global SoC pov, Linux should only
"see" the first 8.
One problem I see is that it's not very robust relying on the relationship
between reg and num-locks. I consider this an implementation detail leaking
into the dt binding and it's not described enough currently...
Going to that future awesome SoCs where it's still called tcsr-mutex, but with
a stride of 4096 bytes makes me wonder; is that really a consecutive 128kb with
nothing else in-between that we can ioremap?
think 64-bit machines with more address space to burn and wanting to separate
resources to use MMUs for protection.
Makes sense, I just don't have any documentation verifying this.
I.e. can we really reuse this driver straight off for that SoC?
I dont see why not.
As long as the space inbetween is just wasted, there is no issue.
Have a look at the msm8916.dtsi in the downstream repository. I think
it'll help with your questions concerning the 0x1000 stride case.
diff --git a/Documentation/devicetree/bindings/hwlock/qcom-hwspinlock.txt b/Documentation/devicetree/bindings/hwlock/qcom-hwspinlock.txt
+- compatible:
+ Usage: required
+ Value type: <string>
+ Definition: must be one of:
+ "qcom,sfpb-mutex",
+ "qcom,tcsr-mutex”
I dont get the purpose of having different compatible strings if there is no
difference in the code between them.
The semantics are the same, but there are no mutex registers in the tcsr block
in e.g 8960, so the name is just missleading. I assume that's why you didn't
follow caf and used the compatible "sfpb" in the first place?
What do you expect the 8960 dt node to look like? I’m not 100% against ‘sfpb’
I’m feel like we we should use compat for stride, so we’d end up with something like:
qcom,sfpb-mutex: stride 4 bytes, base: 0x01200604, reset: 0x01200600
qcom,tcsr-mutex: stride 128 bytes, base: 0xFD484000, reset: 0xFD485380
qcom,tcsr-4k-mutex: stride 4k bytes, base: 0x740000, reset: 0x767000
Maybe these are the best names for the 3 hw blocks after all.
The alternative would be either to encode the platform name in the compatible
or adding the stride as a separate property. The first is waste and the second
doesn't describe how hw is connected. So netiher are good alternatives.
I think your suggestion is reasonable and will move the stride back into
compat. It's the most robust solution.
Is the 4k block finalized (don't see it in 8994 docs)? Should I add it to the
driver now as well?
Thanks for your input!
Regards,
Bjorn
Jeffrey Hugo
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