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From:   Sowjanya Komatineni <skomatineni@nvidia.com>
To:     Mark Brown <broonie@kernel.org>
CC:     "thierry.reding@gmail.com" <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
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        "linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
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Subject: RE: [PATCH V1 18/26] spi: tegra114: add support for hw based cs
Thread-Topic: [PATCH V1 18/26] spi: tegra114: add support for hw based cs
Thread-Index: AQHU5GIKKpTkIfSTtEWeqLFxMgMCeKYm9fSAgAC1kqA=
Date:   Mon, 1 Apr 2019 18:40:36 +0000
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> On Tue, Mar 26, 2019 at 10:56:39PM -0700, Sowjanya Komatineni wrote:
>=20
> > Tegra SPI driver default uses SW CS control for transfers and HW CS=20
> > control can be enabled through SPI client device node DT property=20
> > nvidia,enable-hw-based-cs and is used only for single transfers.
>
> Why have a property - if this feature works and is useful why would a sys=
tem ever not want to use it?

> > +	single_xfer =3D list_is_singular(&msg->transfers);
> >  	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
> >  		u32 cmd1;
> > =20
> >  		reinit_completion(&tspi->xfer_completion);
> > =20
> > -		cmd1 =3D tegra_spi_setup_transfer_one(spi, xfer, is_first_msg);
> > +		cmd1 =3D tegra_spi_setup_transfer_one(spi, xfer, is_first_msg,
> > +						    single_xfer);
>
> It's not sufficient to check if there's only one transfer, you also need =
to make sure that the driver isn't using cs_change to use non-standard chip=
 select handling.

Yes we can avoid DT and force to use HW CS incase of all single transfers w=
ithout cs_change. Will update in next version.