linux-kernel - Re: [PATCH 03/16] dt-bindings: spi: Add spi peripheral specific property

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Date:   Fri, 6 Jan 2023 19:27:34 -0800
From:   William Zhang <william.zhang@...adcom.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Linux SPI List <linux-spi@...r.kernel.org>,
        Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>,
        anand.gore@...adcom.com, tomer.yacoby@...adcom.com,
        dan.beygelman@...adcom.com, joel.peshkin@...adcom.com,
        f.fainelli@...il.com, jonas.gorski@...il.com,
        kursad.oney@...adcom.com, dregan@...l.com,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/16] dt-bindings: spi: Add spi peripheral specific
 property

Hi Mark,

On 01/06/2023 01:14 PM, Mark Brown wrote:
> On Fri, Jan 06, 2023 at 12:07:55PM -0800, William Zhang wrote:
> 
>> brcm,no-clk-gate is a Broadcom Broadband HS SPI controller specific
>> property for certain SPI device such as Broadcom ISI voice daughtercard
>> to work properly. It disables the clock gating feature when the chip
>> select is deasserted for any device that wants to keep the clock
>> running.
> 
> Why would this property be Broadcom specific?  Other devices could in
> theory implement this.
> 
It does not need to be Broadcom specific if other SoC's SPI bus 
controller support such function. I am not aware of such case but 
certainly I am no expert on other chips. I can put it in the generic 
spi-peripheral-props.yaml if that is what you suggest.

>> +properties:
>> +  brcm,no-clk-gate:
>> +    $ref: /schemas/types.yaml#/definitions/flag
>> +    description:
>> +      Some SPI device such as Broadcom ISI based voice daughtercard requires SPI
>> +      clock running even when chip select is deasserted. By default the
>> +      controller turns off or gate the clock when cs is not active to save
>> +      power. This flag tells the controller driver to keep the clock running
>> +      when chip select is not active.
> 
> This seems problematic with any host controlled chip select support...
> 
Yes those ISI chip based voice cards do need such strange requirement 
and will not work with other controller.  That is one of the reason I 
put this as Broadcom specific option.

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