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: <bc88e0c7-516f-4eef-a9d9-ce0250d6a570@baylibre.com>
Date: Mon, 8 Jul 2024 16:15:45 -0500
From: David Lechner <dlechner@...libre.com>
To: Marcelo Schmitt <marcelo.schmitt@...log.com>, broonie@...nel.org,
 lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org,
 robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 nuno.sa@...log.com, corbet@....net, marcelo.schmitt1@...il.com
Cc: 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 6/29/24 2:04 PM, Marcelo Schmitt 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>
> ---

Tested both valid and invalid combinations of flags and saw expected
behavior/error messages in all cases.

Reviewed-by: David Lechner <dlechner@...libre.com>
Tested-by: David Lechner <dlechner@...libre.com>