linux-kernel - Re: [PATCH v4 1/6] spi: Enable controllers to extend the SPI protocol with MOSI idle configuration

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Date: Wed, 19 Jun 2024 12:24:28 -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, marcelo.schmitt1@...il.com
Cc: linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/6] spi: Enable controllers to extend the SPI protocol
 with MOSI idle configuration

On 6/18/24 6:10 PM, Marcelo Schmitt wrote:

...

> @@ -3928,7 +3934,8 @@ int spi_setup(struct spi_device *spi)
>  	 * so it is ignored here.
>  	 */
>  	bad_bits = spi->mode & ~(spi->controller->mode_bits | SPI_CS_WORD |
> -				 SPI_NO_TX | SPI_NO_RX);
> +				 SPI_NO_TX | SPI_NO_RX | SPI_MOSI_IDLE_LOW |
> +				 SPI_MOSI_IDLE_HIGH);

This looks wrong to me. Adding flags here causes them to be ignored
rather than to be checked.

I also did a runtime check with a random driver and a SPI controller
that does not have the flag.

	spi->mode |= SPI_MOSI_IDLE_LOW;
	ret = spi_setup(spi);
	if (ret)
		return ret;

It incorrectly passes when used with this change but correctly fails
without this change.

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