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

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Date:   Mon, 9 Jan 2023 12:18:09 -0800
From:   William Zhang <william.zhang@...adcom.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        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>,
        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 01/09/2023 11:19 AM, Mark Brown wrote:
> On Mon, Jan 09, 2023 at 12:06:13AM -0800, William Zhang wrote:
>>> On Fri, Jan 6, 2023 at 9:27 PM William Zhang <william.zhang@...adcom.com> wrote:
> 
>>> Keeping the clock on or not would affect all devices unless you have a
>>> per device clock you can gate, so making this a per device flag
>>> doesn't make sense.
> 
>> This applies only to each chip select. There is only one device under each
>> chip select.  So won't impact any other devices under other cs.
> 
> I don't understand how this would work - usually a SPI controller has a
> single set of clock, MOSI and MISO lines with the only per device thing
> being the chip select.  If the clock line is used by all devices then it
> must be kept on for all of them if it's to be kept on for one of them.
> 

This setting is set per spi message for particular chip select of the 
device when starting the message through bcm63xx_hsspi_set_clk function 
and restore to default(clock gating) when message is done through 
bcm63xx_hsspi_restore_clk_gate.

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