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

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Date:   Thu, 23 Feb 2023 18:43:13 +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 Thu, Feb 23, 2023 at 06:41:43PM +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?

> > > +		spi_xfer[0].tx_buf = phy->iobuf;
> > > +		spi_xfer[0].len = 1;
> > > +		spi_message_add_tail(&spi_xfer[0], &m);
> > > +
> > > +		spi_xfer[1].tx_buf = phy->iobuf + 1;
> > > +		spi_xfer[1].len = 3;
> > > +		spi_message_add_tail(&spi_xfer[1], &m);

> > Why would we make these two separate transfers?

> Tegra QSPI combined sequence requires cmd, addr and data in different
> transfers. This eliminates need for additional flag for combined sequence.

That needs some documentation, and we might need a flag to ensure the
core doesn't coalesce the transfers.

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