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Message-ID: <d2751939f5813c296cdcb7a92d5698bf@codeaurora.org>
Date: Thu, 01 Feb 2018 12:39:09 -0800
From: Channa <ckadabi@...eaurora.org>
To: Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org,
linux-arm-msm@...r.kernel.org, linux-arm@...ts.infradead.org,
linux-kernel@...r.kernel.org, tsoni@...eaurora.org,
sboyd@...eaurora.org, kyan@...eaurora.org
Subject: Re: [PATCH 1/2] dt-bindings: Documentation for qcom,llcc
On 2018-02-01 02:44, Mark Rutland wrote:
> On Thu, Jan 25, 2018 at 03:55:12PM -0800, Channagoud Kadabi wrote:
>> Documentation for last level cache controller device tree bindings,
>> client bindings usage examples.
>>
>> Signed-off-by: Channagoud Kadabi <ckadabi@...eaurora.org>
>> ---
>> .../devicetree/bindings/arm/msm/qcom,llcc.txt | 93
>> ++++++++++++++++++++++
>> 1 file changed, 93 insertions(+)
>> create mode 100644
>> Documentation/devicetree/bindings/arm/msm/qcom,llcc.txt
>>
>> diff --git a/Documentation/devicetree/bindings/arm/msm/qcom,llcc.txt
>> b/Documentation/devicetree/bindings/arm/msm/qcom,llcc.txt
>> new file mode 100644
>> index 0000000..d433b0c
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/arm/msm/qcom,llcc.txt
>> @@ -0,0 +1,93 @@
>> +* LLCC (Last Level Cache Controller)
>> +
>> +Properties:
>> +- compatible:
>> + Usage: required
>> + Value type: <string>
>> + Definition: must be "qcom,llcc-core"
>> +
>> +- reg:
>> + Usage: required
>> + Value Type: <prop-encoded-array>
>> + Definition: must be addresses and sizes of the LLCC registers
>> +
>> +- llcc-bank-off:
>> + Usage: required
>> + Value Type: <u32 array>
>> + Definition: Offsets of llcc banks from llcc base address starting
>> from
>> + LLCC bank0.
>> +
>> +- llcc-broadcast-off:
>> + Usage: required
>> + Value Type: <u32>
>> + Definition: Offset of broadcast register from LLCC bank0 address.
>
> Please could we use "offset" rather than "off" for both of these? That
> way it's obvious these aren't properties for disabling some feature.
>
> How variable are these offsets in practice? Is the memory map not
> fixed?
The offsets depends on the number of LLCC HW blocks. These number of HW
blocks vary from
chipset to chipset and new registers could be added that changes the
offset.
>
>> +
>> +- #cache-cells:
>> + Usage: required
>> + Value Type: <u32>
>> + Definition: Number of cache cells, must be 1
>
> What's this for, and how is it used?
This is to obtain the phandle arguments from client devices. Related to
cache-slices property.
>
>> +
>> +- max-slices:
>> + usage: required
>> + Value Type: <u32>
>> + Definition: Number of cache slices supported by hardware
>> +
>> +- status:
>> + Usage: optional
>> + Value type: <string>
>> + Definition: Property to enable or disable the driver
>
> This is a standard property, so I don't think it needs to be described
> here.
Sure, will remove it.
>
>> +
>> +== llcc amon device ==
>> +
>> +Properties:
>> +-qcom,fg-cnt : The value of fine grained counter of activity monitor
>> + block.
>
> Could you elaborate on this?
This is counter value programmed in the HW to detect live locks.
This parameter is tunable to avoid false positives.
>
>> +
>> +compatible devices:
>> + qcom,sdm845-llcc
>
> Huh? The "qcom,sdm845-llcc" bindings wasn't described above, and it's
> not clear what this means.
>
>> +
>> +Example:
>> +
>> + qcom,system-cache@...0000 {
>> + compatible = "qcom,llcc-core", "syscon", "simple-mfd";
>
> This looks very wrong. Why do you need syscon and simple-mfd?
LLCC HW block has 3 functionalities:
System cache core, ECC & AMON drivers for debugging.
All three drivers use the same register space for configuration, status
etc.
In order to avoid remapping the same address region across multiple
drivers,
I have implemented this driver as a syncon and simple-mfd.
>
>> + reg = <0x1300000 0x50000>;
>> + reg-names = "llcc_base";
>> +
>> + llcc: qcom,sdm845-llcc {
>> + compatible = "qcom,sdm845-llcc";
>
> Why is this a sub-node?
qcom,sdm845-llcc: This core driver as mentioned in the list above.
>
> Why isn't the top-level node just "qcom,sdm845-llcc" ?
>
>> + #cache-cells = <1>;
>> + max-slices = <32>;
>> + };
>> +
>> + qcom,llcc-ecc {
>> + compatible = "qcom,llcc-ecc";
>> + };
qcom,llcc-ecc: Driver #2 for ECC
>> +
>> + qcom,llcc-amon {
>> + compatible = "qcom,llcc-amon";
>> + qcom,fg-cnt = <0x7>;
>> + };
>> +
qcom,llcc-amon: Driver #3 for AMON
>> + };
>> +
>> +== Client ==
>> +
>> +Properties:
>> +- cache-slice-names:
>> + Usage: required
>> + Value type: <stringlist>
>> + Definition: A set of names that identify the usecase names of a
>> client that uses
>> + cache slice. These strings are used to look up the cache slice
>> + entries by name.
>> +
>> +- cache-slices:
>> + Usage: required
>> + Value type: <prop-encoded-array>
>> + Definition: The tuple has phandle to llcc device as the first
>> argument and the
>> + second argument is the usecase id of the client.
>
> What is a "usecase id" ?
Usecase id for use case that wants to use system cache for eg:
video-encode and video-decode
>
> Is this meant to align with #cache-cells? It would be best to keep a
> common prefix (i.e. call that #cache-slice-cells).
Yes. Will update the name.
>
> Thanks,
> Mark.
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