Re: [PATCH 03/32] spi: dw: Fix driving MOSI low while recieving

Mark Brown
2020-11-09T20:29:25Z

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On Mon, Nov 09, 2020 at 11:17:44PM +0300, Serge Semin wrote:
> On Mon, Nov 09, 2020 at 02:40:01PM -0500, Sean Anderson wrote:
> > On 11/9/20 2:19 PM, Serge Semin wrote:

> > > Getting back to the patch. In fact I don't really see how the
> > > Receive-only mode will help us with solving the problem noted in the
> > > patch log.

> > Shouldn't it put MOSI into High-Z like when the device is idle? The
> > issue is mainly that the idle state and RX state are different.

> AFAICS the manual doesn't say anything about High-Z, but only: "In
> receive-only mode, transmitted data are not valid. After the first
> write to the transmit FIFO, the same word is retransmitted for the
> duration of the transfer."

This is the sort of behaviour I would expect, and I'd expect that going
high Z could potentially cause electrical problems as the line won't be
being driven when it's been designed to be an output from the controller
so it's probably not desirable to do that.

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