linux-kernel - Re: [PATCH 2/2] memory: brcmstb_memc: Simplify compatible matching

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Message-ID: <ac57663b-3bcc-42ae-898e-06592d417715@broadcom.com>
Date: Thu, 5 Jun 2025 12:10:24 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Rob Herring <robh@...nel.org>
Cc: linux-kernel@...r.kernel.org, justin.chen@...adcom.com,
 Krzysztof Kozlowski <krzk@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>,
 "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
 <devicetree@...r.kernel.org>,
 "moderated list:BROADCOM BCM7XXX ARM ARCHITECTURE"
 <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] memory: brcmstb_memc: Simplify compatible matching

On 6/5/25 11:55, Rob Herring wrote:
> On Fri, May 23, 2025 at 11:43:54AM -0700, Florian Fainelli wrote:
>> Now that a "brcm,brcmstb-memc-ddr-rev-b.2.x" fallback compatible string
>> has been defined, we can greatly simplify the matching within the driver
>> to only look for that compatible string and nothing else.
>>
>> The fallback "brcm,brcmstb-memc-ddr" is also updated to assume the V21
>> register layout since that is the most common nowadays.
>>
>> Signed-off-by: Florian Fainelli <florian.fainelli@...adcom.com>
>> ---
>>   drivers/memory/brcmstb_memc.c | 58 ++---------------------------------
>>   1 file changed, 3 insertions(+), 55 deletions(-)
>>
>> diff --git a/drivers/memory/brcmstb_memc.c b/drivers/memory/brcmstb_memc.c
>> index c87b37e2c1f0..ec4c198ddc49 100644
>> --- a/drivers/memory/brcmstb_memc.c
>> +++ b/drivers/memory/brcmstb_memc.c
>> @@ -181,65 +181,13 @@ static const struct of_device_id brcmstb_memc_of_match[] = {
>>   		.data = &brcmstb_memc_versions[BRCMSTB_MEMC_V20]
>>   	},
>>   	{
>> -		.compatible = "brcm,brcmstb-memc-ddr-rev-b.2.1",
>> +		.compatible = "brcm,brcmstb-memc-ddr-rev-b.2.x",
>>   		.data = &brcmstb_memc_versions[BRCMSTB_MEMC_V21]
> 
> This entry is pointless because the default will get V21.
> 
> In fact, I don't think you need the new compatible string at all. It
> doesn't work to add fallbacks after the fact.

I agree and would prefer to keep adding new compatible strings which is 
what I initially did here:

https://lore.kernel.org/all/20241217194439.929040-2-florian.fainelli@broadcom.com/

but the feedback was that this should not be done, and hence this 
attempt at defining a compatible string that would avoid needless churn.

So which way should I go now?
-- 
Florian