linux-kernel - RE: [PATCH V1 18/26] spi: tegra114: add support for hw based cs

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Date:   Mon, 1 Apr 2019 18:40:36 +0000
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Mark Brown <broonie@...nel.org>
CC:     "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Timo Alho <talho@...dia.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "Krishna Yarlagadda" <kyarlagadda@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH V1 18/26] spi: tegra114: add support for hw based cs

> On Tue, Mar 26, 2019 at 10:56:39PM -0700, Sowjanya Komatineni wrote:
> 
> > Tegra SPI driver default uses SW CS control for transfers and HW CS 
> > control can be enabled through SPI client device node DT property 
> > 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 system ever not want to use it?

> > +	single_xfer = list_is_singular(&msg->transfers);
> >  	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
> >  		u32 cmd1;
> >  
> >  		reinit_completion(&tspi->xfer_completion);
> >  
> > -		cmd1 = tegra_spi_setup_transfer_one(spi, xfer, is_first_msg);
> > +		cmd1 = 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 without cs_change. Will update in next version.