linux-kernel - Re: [Patch V3 1/3] tpm_tis-spi: Support hardware wait polling

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Date:   Fri, 24 Feb 2023 15:51:41 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Krishna Yarlagadda <kyarlagadda@...dia.com>
Cc:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "peterhuewe@....de" <peterhuewe@....de>,
        "jgg@...pe.ca" <jgg@...pe.ca>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "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 V3 1/3] tpm_tis-spi: Support hardware wait polling

On Fri, Feb 24, 2023 at 02:16:27PM +0000, Krishna Yarlagadda wrote:

> > > > > +       spi_bus_lock(phy->spi_device->master);
> > > > > +
> > > > > +       while (len) {

> > > > Why?

> > > TPM supports max 64B in single transaction. Loop to send rest of it.

> > No, why is there a bus lock?

> Bus lock to avoid other clients to be accessed between TPM transfers.

That's what a bus lock does but what would be the problem if something
else sent a message between messages?  Note that a message will always
be sent atomically.

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