linux-kernel - Re: [PATCH 2/3] spi: tegra210-quad: Add wait polling support

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Date:   Thu, 17 Mar 2022 18:09:33 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Krishna Yarlagadda <kyarlagadda@...dia.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Ashish Singhal <ashishsingha@...dia.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] spi: tegra210-quad: Add wait polling support

On Thu, Mar 17, 2022 at 06:00:25PM +0000, Krishna Yarlagadda wrote:

> > >> Wait polling still has to be selected on slave devices that can
> > >> support it.
> > >> I will add one line description for the properties in next version.

> > > I can't say I am familiar with this, but it seems that the ideal
> > > solution would be able to detect if this needs to be enabled depending
> > > on the device connected. Is that not possible?

> We cannot detect at runtime which slave supports wait polling.

How would the client device have any knowledge of how the controller
internal implementation works?  What even is a "wait state inserted by
TPM device"?  If this is something the client device is doing then it
should be something that is expressed through the generic SPI API by the
client device, if some controllers have some way of optimising this then
we can add support for that but presumably it's just something that's
generically supported by that device so we shouldn't need a DT property
for it on the device side either.

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