Message-ID: <48902771-5d3b-448a-8a74-ac18fb4f1a86@linaro.org>
Date: Tue, 5 Mar 2024 08:43:03 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Markus Schneider-Pargmann <msp@...libre.com>
Cc: Rob Herring <robh@...nel.org>, Nishanth Menon <nm@...com>,
 Vignesh Raghavendra <vigneshr@...com>, Tero Kristo <kristo@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
 Santosh Shilimkar <ssantosh@...nel.org>, Andrew Davis <afd@...com>,
 linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] dt-bindings: hwinfo: ti,k3-socinfo: Add nvmem-cells

On 04/03/2024 11:36, Markus Schneider-Pargmann wrote:
> Hi,
> 
> On Sat, Feb 17, 2024 at 03:25:30PM +0100, Krzysztof Kozlowski wrote:
>> On 14/02/2024 10:31, Markus Schneider-Pargmann wrote:
>>> Hi Rob,
>>>
>>> On Tue, Feb 06, 2024 at 06:43:05PM +0000, Rob Herring wrote:
>>>> On Tue, Feb 06, 2024 at 03:37:09PM +0100, Markus Schneider-Pargmann wrote:
>>>>> The information k3-socinfo requires is stored in an efuse area. This
>>>>> area is required by other devices/drivers as well, so using nvmem-cells
>>>>> can be a cleaner way to describe which information are used.
>>>>>
>>>>> If nvmem-cells are supplied, the address range is not required.
>>>>> Cells chipvariant, chippartno and chipmanufacturer are introduced to
>>>>> cover all required information.
>>>>>
>>>>> Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
>>>>> Reviewed-by: Andrew Davis <afd@...com>
>>>>> ---
>>>>>  .../bindings/hwinfo/ti,k3-socinfo.yaml        | 23 ++++++++++++++++++-
>>>>>  1 file changed, 22 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/hwinfo/ti,k3-socinfo.yaml b/Documentation/devicetree/bindings/hwinfo/ti,k3-socinfo.yaml
>>>>> index dada28b47ea0..f085b7275b7d 100644
>>>>> --- a/Documentation/devicetree/bindings/hwinfo/ti,k3-socinfo.yaml
>>>>> +++ b/Documentation/devicetree/bindings/hwinfo/ti,k3-socinfo.yaml
>>>>> @@ -26,9 +26,24 @@ properties:
>>>>>    reg:
>>>>>      maxItems: 1
>>>>>  
>>>>> +  nvmem-cells:
>>>>> +    $ref: /schemas/types.yaml#/definitions/phandle-array
>>>>> +
>>>>> +  nvmem-cell-names:
>>>>> +    items:
>>>>> +      - const: chipvariant
>>>>> +      - const: chippartno
>>>>> +      - const: chipmanufacturer
>>>>> +
>>>>>  required:
>>>>>    - compatible
>>>>> -  - reg
>>>>> +
>>>>> +oneOf:
>>>>> +  - required:
>>>>> +      - reg
>>>>> +  - required:
>>>>> +      - nvmem-cells
>>>>> +      - nvmem-cell-names
>>>>>  
>>>>>  additionalProperties: false
>>>>>  
>>>>> @@ -38,3 +53,9 @@ examples:
>>>>>          compatible = "ti,am654-chipid";
>>>>>          reg = <0x43000014 0x4>;
>>>>>      };
>>>>> +  - |
>>>>> +    chipid: chipid@14 {
>>>>> +        compatible = "ti,am654-chipid";
>>>>
>>>> This isn't compatible if you have a completely different way to access 
>>>> it. 
>>>
>>> Thanks, it is not entirely clear to me how I could go forward with this?
>>> Are you suggesting to use a different compatible? Or is it something
>>> else I could do to proceed with this conversion?
>>
>> What you claim now, is that you have one device with entirely different
>> interfaces and programming model. So either this is not the same device
>> or you just wrote bindings to whatever you have in driver.
>>
>> Nothing in commit msg explains this.
>>
>> What you should do? Depends. If you just write bindings for driver, then
>> stop. It's a NAK. Instead write bindings for hardware.
>>
>> If the first choice, just the hardware is somehow like this, then
>> explain in commit msg and device description, how this device can be
>> connected over other bus, not MMIO. You can draw some schematics in
>> commit msg explaining architecture etc.
> 
> Sorry the information provided in the commit message is not very clear.
> 
> The basic access to the registes is still MMIO. nvmem is used to have a
> better abstraction and cleaner description of the hardware.
> 
> Currently most of the data is exported using the parent syscon device.
> The relevant data is read-only and contained in a single register with
> offset 0x14:
>   - Chip variant
>   - Chip part number
>   - Chip manufacturer
> 
> There are more read-only registers in this section of address space.
> These are relevant to other components as they define the operating
> points for example. For the OPP table relevant are chip variant and chip
> speed (which is in a different register).
> 
> Instead of devices refering to this whole register range of 0x20000 in

Whaaaaat?

> size, I would like to introduce this nvmem abstraction in between that
> describes the information and can directly be referenced by the devices
> that depend on it. In this case the above mentioned register with offset
> 0x14 is instead described as nvmem-layout like this:
> 
> 	nvmem-layout {
> 		compatible = "fixed-layout";
> 		#address-cells = <1>;
> 		#size-cells = <1>;
> 
> 		chip_manufacturer: jtagidmfg@14 {
> 			reg = <0x14 0x2>;
> 			bits = <1 11>;
> 		};
> 
> 		chip_partno: jtagidpartno@15 {
> 			reg = <0x15 0x3>;
> 			bits = <4 16>;
> 		};
> 
> 		chip_variant: jtagidvariant@17 {
> 			reg = <0x17 0x1>;
> 			bits = <4 4>;
> 		};
> 
> 		chip_speed: jtaguseridspeed@18 {
> 			reg = <0x18 0x4>;
> 			bits = <6 5>;
> 		};
> 
> The underlying registers are still the same but they are not hidden
> by the syscon phandles anymore.
> 
> The device that consumes this data would now use
> 
> 	nvmem-cells = <&chip_variant>, <&chip_speed>;
> 	nvmem-cell-names = "chipvariant", "chipspeed";
> 
> instead of
> 
> 	syscon = <&wkup_conf>;

syscon allows you this as well - via phandle arguments.

nvmem is for non-volatile memory, like OCOTP and eFUSE. This is not for
accessing regular MMIO registers of system-controller, regardless
whether they are read-only or not (regmap handles this nicely, BTW).
Although probably Apple efuses and few others can confuse here. It still
looks like you convert regular system-controller block into nvmem,
because you prefer that Linux driver abstraction...

Best regards,
Krzysztof

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