linux-kernel - Re: [Patch V5 2/3] tpm_tis-spi: Support hardware wait polling

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Message-ID: <Y/9HB/KF2Kjkihkg@sirena.org.uk>
Date:   Wed, 1 Mar 2023 12:37:27 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Krishna Yarlagadda <kyarlagadda@...dia.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "peterhuewe@....de" <peterhuewe@....de>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>
Subject: Re: [Patch V5 2/3] tpm_tis-spi: Support hardware wait polling

On Wed, Mar 01, 2023 at 08:27:45AM -0400, Jason Gunthorpe wrote:
> On Wed, Mar 01, 2023 at 11:56:53AM +0000, Krishna Yarlagadda wrote:

> > TPM device connected behind half duplex controller can only work
> > this way. So, no additional flag needed to check.

> Just because a DT hooks it up this way doesn't mean the kernel driver
> can support it, eg support hasn't been implemented in an older SPI
> driver or something.

> If the failure mode is anything other than the TPM doesn't probe we
> will need to check for support.

It's not like these buses are hot pluggable - someone would have to
design and manufacture a board which doesn't work.  It's probably
reasonable for this to fail with the SPI subsystem saying it can't
support things when the operation is tried.

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