From:   Krishna Yarlagadda <kyarlagadda@nvidia.com>
To:     Mark Brown <broonie@kernel.org>
CC:     "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "peterhuewe@gmx.de" <peterhuewe@gmx.de>,
        "jgg@ziepe.ca" <jgg@ziepe.ca>,
        "jarkko@kernel.org" <jarkko@kernel.org>,
        "krzysztof.kozlowski+dt@linaro.org" 
        <krzysztof.kozlowski+dt@linaro.org>,
        "linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        "linux-integrity@vger.kernel.org" <linux-integrity@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "thierry.reding@gmail.com" <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Sowjanya Komatineni <skomatineni@nvidia.com>,
        Laxman Dewangan <ldewangan@nvidia.com>
Subject: RE: [Patch V3 1/3] tpm_tis-spi: Support hardware wait polling
Thread-Topic: [Patch V3 1/3] tpm_tis-spi: Support hardware wait polling
Thread-Index: AQHZR6OqOBQhj0zBTUWL/FYm6RTrP67cxooAgAAUpuCAAALmgIABQ3fw
Date:   Fri, 24 Feb 2023 14:16:27 +0000
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References: <20230223162635.19747-1-kyarlagadda@nvidia.com>
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> -----Original Message-----
> From: Mark Brown <broonie@kernel.org>
> Sent: 24 February 2023 00:13
> To: Krishna Yarlagadda <kyarlagadda@nvidia.com>
> Cc: robh+dt@kernel.org; peterhuewe@gmx.de; jgg@ziepe.ca;
> jarkko@kernel.org; krzysztof.kozlowski+dt@linaro.org; linux-
> spi@vger.kernel.org; linux-tegra@vger.kernel.org; linux-
> integrity@vger.kernel.org; linux-kernel@vger.kernel.org;
> thierry.reding@gmail.com; Jonathan Hunter <jonathanh@nvidia.com>;
> Sowjanya Komatineni <skomatineni@nvidia.com>; Laxman Dewangan
> <ldewangan@nvidia.com>
> Subject: Re: [Patch V3 1/3] tpm_tis-spi: Support hardware wait polling
>=20
> On Thu, Feb 23, 2023 at 06:41:43PM +0000, Krishna Yarlagadda wrote:
>=20
> > > > +       spi_bus_lock(phy->spi_device->master);
> > > > +
> > > > +       while (len) {
>=20
> > > Why?
>=20
> > TPM supports max 64B in single transaction. Loop to send rest of it.
>=20
> No, why is there a bus lock?
Bus lock to avoid other clients to be accessed between TPM transfers.

>=20
> > > > +		spi_xfer[0].tx_buf =3D phy->iobuf;
> > > > +		spi_xfer[0].len =3D 1;
> > > > +		spi_message_add_tail(&spi_xfer[0], &m);
> > > > +
> > > > +		spi_xfer[1].tx_buf =3D phy->iobuf + 1;
> > > > +		spi_xfer[1].len =3D 3;
> > > > +		spi_message_add_tail(&spi_xfer[1], &m);
>=20
> > > Why would we make these two separate transfers?
>=20
> > Tegra QSPI combined sequence requires cmd, addr and data in different
> > transfers. This eliminates need for additional flag for combined sequen=
ce.
>=20
> That needs some documentation, and we might need a flag to ensure the
> core doesn't coalesce the transfers.
Will add comment at top of the function. Bus lock should avoid coalesce of
transfer of single message from others.
KY