linux-kernel - Re: [PATCH 1/2] dt-bindings: fpga: zynq: Document ICAP on boot

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Message-ID: <14b12882-119d-4c24-9634-e4cc37a39212@kernel.org>
Date: Mon, 31 Mar 2025 14:43:59 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Sam Winchenbach <sam.winchenbach@...mepointer.org>
Cc: linux-kernel@...r.kernel.org, mdf@...nel.org, hao.wu@...el.com,
 yilun.xu@...el.com, trix@...hat.com, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, michal.simek@....com, linux-fpga@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 Sam Winchenbach <swinchenbach@...a.org>
Subject: Re: [PATCH 1/2] dt-bindings: fpga: zynq: Document ICAP on boot

On 31/03/2025 14:30, Sam Winchenbach wrote:
>>
>>> +    type: boolean
>>> +    description: If present, the ICAP controller will be enabled when
>>> +      the driver probes. This is useful if the fabric is loaded
>>> +      during the boot process and contains a core, such as the SEM,
>>
>> I don't get how this is suitable for DT. If you decide to load the
>> fabric from driver, that's driver decision so not DT.
> 
> Before writing the fabric to the FPGA the driver disables the ICAP, enabling
> the PCAP. Once writing is complete it unconditionally disables the PCAP,
> enabling the ICAP. This patch just makes it so, depending on the use case,
> the ICAP can be enabled at boot. This will not prevent the system from being
> able to load a fabric through the driver. I added in this boolean so existing
> behavior would be maintained.
> 
> Do you recommend another approach such as writing to a sysfs attribute to
> switch from PCAP to ICAP?
Not sure yet. Can't you check the status of ICAP before programming and
then enable it only if was enabled before?

Best regards,
Krzysztof