linux-kernel - Re: [PATCH] spi: fix cs

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Date:   Mon, 16 Mar 2020 12:17:50 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi: fix cs_change for last transfer

On Sun, Mar 15, 2020 at 06:08:53PM +0100, Michał Mirosław wrote:

> Generic spi_transfer_one_message() implementation introduced in
> commit b158935f70b9 has a bug in cs_change handling: it keeps CS
> asserted when cs_change is set. Fix it.

>  	struct spi_transfer *xfer;
> -	bool keep_cs = false;
> +	bool keep_cs = true;
>  	int ret = 0;
>  	struct spi_statistics *statm = &ctlr->statistics;
>  	struct spi_statistics *stats = &msg->spi->statistics;
> @@ -1268,7 +1268,7 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
>  		if (xfer->cs_change) {
>  			if (list_is_last(&xfer->transfer_list,
>  					 &msg->transfers)) {
> -				keep_cs = true;
> +				keep_cs = false;
>  			} else {

This is the opposite of the intended behaviour - we want to deassert
chip select at the end of the message unless cs_change is set on the
last transfer.  If this were broken I would expect to see widespread
problems being reported.

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