linux-kernel - Re: [PATCH 1/2] dt-bindings: memory-controller: Document rev c.1.5 compatible

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Message-ID: <93a1333d-442f-4cec-b823-9b1a5ff6dc6b@broadcom.com>
Date: Wed, 18 Dec 2024 09:15:08 -0800
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, Rob Herring <robh@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>,
 "open list:MEMORY CONTROLLER DRIVERS" <linux-kernel@...r.kernel.org>,
 "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
 <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: memory-controller: Document rev c.1.5
 compatible

On 12/18/24 03:37, Krzysztof Kozlowski wrote:
> On Tue, Dec 17, 2024 at 11:44:38AM -0800, Florian Fainelli wrote:
>> Document the revision c.1.5 compatible string that is present on newer
>> Broadcom STB memory controllers (74165 and onwards).
>>
>> Signed-off-by: Florian Fainelli <florian.fainelli@...adcom.com>
>> ---
>>   .../bindings/memory-controllers/brcm,brcmstb-memc-ddr.yaml       | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/Documentation/devicetree/bindings/memory-controllers/brcm,brcmstb-memc-ddr.yaml b/Documentation/devicetree/bindings/memory-controllers/brcm,brcmstb-memc-ddr.yaml
>> index 4b072c879b02..99d79ccd1036 100644
>> --- a/Documentation/devicetree/bindings/memory-controllers/brcm,brcmstb-memc-ddr.yaml
>> +++ b/Documentation/devicetree/bindings/memory-controllers/brcm,brcmstb-memc-ddr.yaml
>> @@ -29,6 +29,7 @@ properties:
>>             - brcm,brcmstb-memc-ddr-rev-c.1.2
>>             - brcm,brcmstb-memc-ddr-rev-c.1.3
>>             - brcm,brcmstb-memc-ddr-rev-c.1.4
>> +          - brcm,brcmstb-memc-ddr-rev-c.1.5
> 
> You should use v2.1 fallback and drop driver patch. Or explain in
> commit briefly why different approach is suitable.

Are you suggesting that we should have fallback compatible strings, such 
that we have something like this:

compatible = "brcm,brcmstb-memc-ddr-rev-c.1.5", 
"brcm,brcmstb-memc-ddr-rev-c", "brcm,brcmstb-memc-ddr"

and the driver only needs to match on "brcm,brcmstb-memc-ddr-rev-c" and 
apply the adequate register offset table?

If so, that is not how the current binding, and therefore DTBs are being 
deployed, so that will introduce a breakage until we update all DTBs in 
the field...
-- 
Florian