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

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Message-ID: <20190401074857.GK2059@sirena.org.uk>
Date:   Mon, 1 Apr 2019 14:48:57 +0700
From:   Mark Brown <broonie@...nel.org>
To:     Sowjanya Komatineni <skomatineni@...dia.com>
Cc:     thierry.reding@...il.com, jonathanh@...dia.com, talho@...dia.com,
        robh+dt@...nel.org, mark.rutland@....com, kyarlagadda@...dia.com,
        ldewangan@...dia.com, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-spi@...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.

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