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Subject: Re: [PATCH v2 01/10] dt-bindings: mtd: brcmnand: Updates for bcmbca
 SoCs
To: Conor Dooley <conor@kernel.org>, dregan@broadcom.com
Cc: dregan@mail.com, miquel.raynal@bootlin.com, richard@nod.at,
 vigneshr@ti.com, robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org,
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 linux-kernel@vger.kernel.org, joel.peshkin@broadcom.com,
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 florian.fainelli@broadcom.com, rafal@milecki.pl,
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 baruch@tkos.co.il, linux-arm-kernel@lists.infradead.org,
 dan.carpenter@linaro.org
References: <20240118195356.133391-1-dregan@broadcom.com>
 <20240118195356.133391-2-dregan@broadcom.com>
 <20240119-retiree-fanciness-0f7bb37c4633@spud>
From: William Zhang <william.zhang@broadcom.com>
Message-ID: <3a87d0ac-f124-7db9-2a69-626cdc7f11ad@broadcom.com>
Date: Fri, 19 Jan 2024 10:36:13 -0800
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Hi,

On 01/19/2024 09:12 AM, Conor Dooley wrote:
> On Thu, Jan 18, 2024 at 11:53:47AM -0800, dregan@broadcom.com wrote:
>> From: William Zhang <william.zhang@broadcom.com>
>>
>> Update the descriptions to reflect different families of broadband SoC and
>> use the general name bcmbca for ARM based SoC.
>>
>> Add brcm,nand-use-wp property to have an option for disabling this
>> feature on broadband board design that does not use write protection.
>>
>> Add brcm,nand-ecc-use-strap to get ecc setting from board boot strap for
>> broadband board designs because they do not specify ecc setting in dts
>> but rather using the strap setting.
>>
>> Remove the requirement of interrupts property to reflect the driver
>> code. Also add myself to the list of maintainers.
>>
>> Signed-off-by: William Zhang <william.zhang@broadcom.com>
>> Reviewed-by: David Regan <dregan@broadcom.com>
>> ---
>> Changes in v2:
>> - Revert the new compatible string nand-bcmbca
>> - Drop the BCM63168 compatible fix to avoid any potential ABI
>> incompatibility issue
>> - Simplify the explanation for brcm,nand-use-wp
>> - Keep the interrupt name requirement when interrupt number is specified
>> ---
>>   .../bindings/mtd/brcm,brcmnand.yaml           | 36 +++++++++++++++----
>>   1 file changed, 30 insertions(+), 6 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/mtd/brcm,brcmnand.yaml b/Documentation/devicetree/bindings/mtd/brcm,brcmnand.yaml
>> index f57e96374e67..56176ec1a992 100644
>> --- a/Documentation/devicetree/bindings/mtd/brcm,brcmnand.yaml
>> +++ b/Documentation/devicetree/bindings/mtd/brcm,brcmnand.yaml
>> @@ -9,6 +9,7 @@ title: Broadcom STB NAND Controller
>>   maintainers:
>>     - Brian Norris <computersforpeace@gmail.com>
>>     - Kamal Dasu <kdasu.kdev@gmail.com>
>> +  - William Zhang <william.zhang@broadcom.com>
>>   
>>   description: |
>>     The Broadcom Set-Top Box NAND controller supports low-level access to raw NAND
>> @@ -18,9 +19,10 @@ description: |
>>     supports basic PROGRAM and READ functions, among other features.
>>   
>>     This controller was originally designed for STB SoCs (BCM7xxx) but is now
>> -  available on a variety of Broadcom SoCs, including some BCM3xxx, BCM63xx, and
>> -  iProc/Cygnus. Its history includes several similar (but not fully register
>> -  compatible) versions.
>> +  available on a variety of Broadcom SoCs, including some BCM3xxx, MIPS based
>> +  Broadband SoC (BCM63xx), ARM based Broadband SoC (BCMBCA) and iProc/Cygnus.
>> +  Its history includes several similar (but not fully register compatible)
>> +  versions.
>>   
>>     -- Additional SoC-specific NAND controller properties --
>>   
>> @@ -53,7 +55,7 @@ properties:
>>                 - brcm,brcmnand-v7.2
>>                 - brcm,brcmnand-v7.3
>>             - const: brcm,brcmnand
>> -      - description: BCM63138 SoC-specific NAND controller
>> +      - description: BCMBCA SoC-specific NAND controller
>>           items:
>>             - const: brcm,nand-bcm63138
>>             - enum:
>> @@ -65,7 +67,7 @@ properties:
>>             - const: brcm,nand-iproc
>>             - const: brcm,brcmnand-v6.1
>>             - const: brcm,brcmnand
>> -      - description: BCM63168 SoC-specific NAND controller
>> +      - description: BCM63xx SoC-specific NAND controller
>>           items:
>>             - const: brcm,nand-bcm63168
>>             - const: brcm,nand-bcm6368
>> @@ -111,6 +113,17 @@ properties:
>>         earlier versions of this core that include WP
>>       type: boolean
>>   
>> +  brcm,nand-use-wp:
>> +    description:
>> +      Use this property to indicate if board design uses
>> +      controller's write protection feature and connects its
>> +      NAND_WPb pin to nand chip's WP_L pin. Driver defaults to
>> +      use this feature when this property does not exist.
>> +      Set to 0 if WP pins are not connected and feature is not
>> +      used. Set to 1 if WP pins are connected and feature is used.
>> +    $ref: /schemas/types.yaml#/definitions/uint32
>> +    enum: [0, 1]
> 
> This property does not make sense to me. "Driver defaults to use this
> feature when the property does not exist" - either the property name is
> backwards or the description is. Secondly, I don't get why the property
> is an enum in the first place - depending on which if the name or
> description is wrong, either 0 or 1 would overlap with the default.
> 
The write protection feature was controlled by the module parameter 
wp_on with default set to enabled. But not all the board use this 
feature especially in BCMBCA broadband board. And module parameter is 
not sufficient as different board can have different option.  Add a 
device tree property to override this default behavior and allow this 
feature to be configured through the board dts on per board basis.

Maybe I can update the text here to
"By default the driver use a module parameter with default value set to 
enable to control this feature for all boards.  Use this dts property to 
override the default behavior and enable/disable this feature through 
board dts on per board basis"

>>   patternProperties:
>>     "^nand@[a-f0-9]$":
>>       type: object
>> @@ -137,6 +150,16 @@ patternProperties:
>>             layout.
>>           $ref: /schemas/types.yaml#/definitions/uint32
>>   
>> +      brcm,nand-ecc-use-strap:
>> +        description:
>> +          This flag is used by the driver to get the ecc strength and
>> +          spare area size from the SoC NAND boot strap setting. This
>> +          is commonly used by the BCMBCA SoC board design. If ecc
>> +          strength and spare area size are set by nand-ecc-strength
>> +          and brcm,nand-oob-sector-size in the dts, these settings
>> +          have precedence and override this flag.
>> +        $ref: /schemas/types.yaml#/definitions/flag
> 
> This property I'm not all that sure about either. If the specific
> properties that you mention here are not set in the DT what happens at
> the moment?
> 
In that case, the ecc strength and oob size come from ONFI or nand id 
decoding.  But that is usually the minimum requirement and user can 
choose to use stronger ecc as long as there is enough oob spare area in 
the nand chip.

> I suppose what I am getting at is why are the bootstrap settings not
> always used in the absence of specific values provided in the DT?
> 
This is because the STB, iProc and other chip and their board design may 
not have or use the strap setting. But for BCMBCA SoC and board 
reference design, we always use the strap setting.

> Thanks,
> Conor.
> 
>> +
>>       unevaluatedProperties: false
>>   
>>   allOf:
>> @@ -177,6 +200,8 @@ allOf:
>>               - const: iproc-idm
>>               - const: iproc-ext
>>     - if:
>> +      required:
>> +        - interrupts
>>         properties:
>>           interrupts:
>>             minItems: 2
>> @@ -189,7 +214,6 @@ unevaluatedProperties: false
>>   required:
>>     - reg
>>     - reg-names
>> -  - interrupts
>>   
>>   examples:
>>     - |
>> -- 
>> 2.37.3
>>

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