linux-kernel - Re: [PATCH v6 1/7] spi: Enable controllers to extend the SPI protocol with MOSI idle configuration

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Message-ID: <20240630114716.3e06f18b@jic23-huawei>
Date: Sun, 30 Jun 2024 11:47:16 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Marcelo Schmitt <marcelo.schmitt@...log.com>
Cc: <broonie@...nel.org>, <lars@...afoo.de>, <Michael.Hennerich@...log.com>,
 <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
 <conor+dt@...nel.org>, <nuno.sa@...log.com>, <dlechner@...libre.com>,
 <corbet@....net>, <marcelo.schmitt1@...il.com>,
 <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
 <linux-spi@...r.kernel.org>, <linux-doc@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 1/7] spi: Enable controllers to extend the SPI
 protocol with MOSI idle configuration

On Sat, 29 Jun 2024 16:04:40 -0300
Marcelo Schmitt <marcelo.schmitt@...log.com> wrote:

> The behavior of an SPI controller data output line (SDO or MOSI or COPI
> (Controller Output Peripheral Input) for disambiguation) is usually not
> specified when the controller is not clocking out data on SCLK edges.
> However, there do exist SPI peripherals that require specific MOSI line
> state when data is not being clocked out of the controller.
> 
> Conventional SPI controllers may set the MOSI line on SCLK edges then bring
> it low when no data is going out or leave the line the state of the last
> transfer bit. More elaborated controllers are capable to set the MOSI idle
> state according to different configurable levels and thus are more suitable
> for interfacing with demanding peripherals.
> 
> Add SPI mode bits to allow peripherals to request explicit MOSI idle state
> when needed.
> 
> When supporting a particular MOSI idle configuration, the data output line
> state is expected to remain at the configured level when the controller is
> not clocking out data. When a device that needs a specific MOSI idle state
> is identified, its driver should request the MOSI idle configuration by
> setting the proper SPI mode bit.
> 
> Acked-by: Nuno Sa <nuno.sa@...log.com>
> Signed-off-by: Marcelo Schmitt <marcelo.schmitt@...log.com>

I always like to see some nice ascii art. Very nice documentation.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 93f59ebb5b79..c8ba5e490850 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c

> @@ -3950,6 +3956,7 @@ int spi_setup(struct spi_device *spi)
>  	 */
>  	bad_bits = spi->mode & ~(spi->controller->mode_bits | SPI_CS_WORD |
>  				 SPI_NO_TX | SPI_NO_RX);
> +

Trivial grumpy comment.  Don't touch white space in unrelated code!

>  	ugly_bits = bad_bits &
>  		    (SPI_TX_DUAL | SPI_TX_QUAD | SPI_TX_OCTAL |
>  		     SPI_RX_DUAL | SPI_RX_QUAD | SPI_RX_OCTAL);