From:   Krishna Yarlagadda <kyarlagadda@nvidia.com>
To:     Jason Gunthorpe <jgg@nvidia.com>,
        Jarkko Sakkinen <jarkko@kernel.org>
CC:     "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "broonie@kernel.org" <broonie@kernel.org>,
        "peterhuewe@gmx.de" <peterhuewe@gmx.de>,
        "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 V5 2/3] tpm_tis-spi: Support hardware wait polling
Thread-Topic: [Patch V5 2/3] tpm_tis-spi: Support hardware wait polling
Thread-Index: AQHZSqQUcW4yC19F/EyRW9qbZsaOO67jpaAAgAClToCAAYhzAA==
Date:   Wed, 1 Mar 2023 11:56:53 +0000
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References: <20230227120702.13180-1-kyarlagadda@nvidia.com>
 <20230227120702.13180-3-kyarlagadda@nvidia.com> <Y/1oqr0RfD7KVA4y@kernel.org>
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> -----Original Message-----
> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: 28 February 2023 17:58
> To: Jarkko Sakkinen <jarkko@kernel.org>
> Cc: Krishna Yarlagadda <kyarlagadda@nvidia.com>; robh+dt@kernel.org;
> broonie@kernel.org; peterhuewe@gmx.de;
> 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 V5 2/3] tpm_tis-spi: Support hardware wait polling
>=20
> On Tue, Feb 28, 2023 at 04:36:26AM +0200, Jarkko Sakkinen wrote:
> > On Mon, Feb 27, 2023 at 05:37:01PM +0530, Krishna Yarlagadda wrote:
> > > TPM devices raise wait signal on last addr cycle. This can be detecte=
d
> > > by software driver by reading MISO line on same clock which requires
> > > full duplex support. In case of half duplex controllers wait detectio=
n
> > > has to be implemented in HW.
> > > Support hardware wait state detection by sending entire message and l=
et
> > > controller handle flow control.
> >
> > When a is started sentence with the word "support" it translates to "I'=
m
> > too lazy to write a proper and verbose description of the implementatio=
n"
> > :-)
> >
> > It has some abstract ideas of the implementation, I give you that, but =
do
> > you think anyone ever will get any value of reading that honestly? A bi=
t
> > more concrette description of the change helps e.g. when bisecting bugs=
.
>=20
> I would expect SPI_TPM_HW_FLOW to be documented in the kdocs to a
> level that any other HW could implement it as well.
HW implementation can be controller specific. I would add comments in the
header to say CMD-ADDR-DATA is sent as single message with this flag.
>=20
> > > +int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 le=
n,
> > > +			 u8 *in, const u8 *out)
> > > +{
> > > +	struct tpm_tis_spi_phy *phy =3D to_tpm_tis_spi_phy(data);
> > > +	struct spi_controller *ctlr =3D phy->spi_device->controller;
> > > +
> > > +	/*
> > > +	 * TPM flow control over SPI requires full duplex support.
> > > +	 * Send entire message to a half duplex controller to handle
> > > +	 * wait polling in controller.
> > > +	 * Set TPM HW flow control flag..
> > > +	 */
> > > +	if (ctlr->flags & SPI_CONTROLLER_HALF_DUPLEX) {
> > > +		phy->spi_device->mode |=3D SPI_TPM_HW_FLOW;
>=20
> Shouldn't we check that this special flow is supported when the SPI
> device is bound to the tpm in the first place?
TPM device connected behind half duplex controller can only work
this way. So, no additional flag needed to check.
KY
>=20
> Jason