Re: [PATCH] iio: adc: ti-ads7950: Ensure CS is deasserted after reading channels

[Mark Brown <broonie@kernel.org>]

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On Sat, Jul 10, 2021 at 10:32:46AM -0500, David Lechner wrote:
> On 7/10/21 7:18 AM, Uwe Kleine-König wrote:

> > If it's not broken for you without my patch, your spi bus driver doesn't
> > honor .cs_change in the last transfer. Out of interest: Which bus are
> > you using? I wonder if the driver should refuse the request if it cannot
> > honer .cs_change?! (spi-imx does honor it only if gpios are used as chip
> > select, the native chip selects cannot do that.)

> I'm using spi-davinci. It uses the standard spi_transfer_one_message()
> which handles cs_change. But I suspect when the SPI_CS_WORD flag is set,
> and the message is big enough to use DMA, the hardware is probably
> automatically toggling CS after the last transfer before the cs_change
> logic asserts it again.

> So unless there is a valid use case where we need both SPI_CS_WORD
> and cs_change, I don't think we need to fix spi-davinci.

In theory it does mean something, in practice the number of controllers
that can implement it must be approaching zero.

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