linux-kernel - Re: [PATCH v4 3/8] spi: stm32: Add 'SPI_SIMPLEX_RX', 'SPI_3WIRE

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Date:   Fri, 22 May 2020 23:59:25 +0800
From:   dillon min <dillon.minfei@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>, p.zabel@...gutronix.de,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Alexandre Torgue <alexandre.torgue@...com>,
        thierry.reding@...il.com, Sam Ravnborg <sam@...nborg.org>,
        Dave Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        "open list:DRM PANEL DRIVERS" <dri-devel@...ts.freedesktop.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v4 3/8] spi: stm32: Add 'SPI_SIMPLEX_RX', 'SPI_3WIRE_RX'
 support for stm32f4

On Fri, May 22, 2020 at 10:57 PM dillon min <dillon.minfei@...il.com> wrote:
>
> hi Mark,
>
> Thanks for reviewing.
>
> On Fri, May 22, 2020 at 7:36 PM Mark Brown <broonie@...nel.org> wrote:
> >
> > On Mon, May 18, 2020 at 07:09:20PM +0800, dillon.minfei@...il.com wrote:
> >
> > > 2, use stm32 spi's "In full-duplex (BIDIMODE=0 and RXONLY=0)", as tx_buf is
> > > null, we must add dummy data sent out before read data.
> > > so, add stm32f4_spi_tx_dummy() to handle this situation.
> >
> > There are flags SPI_CONTROLLER_MUST_TX and SPI_CONTROLLER_MUST_RX flags
> > that the driver can set if it needs to, no need to open code this in the
> > driver.
>
> Yes, after check SPI_CONTROLLER_MUST_TX in drivers/spi/spi.c , it's
> indeed to meet
> this situation,  i will try it and sumbmit a new patch.
>
> thanks.
>
> best regards
>
> Dillon

Hi Mark,

There might be a conflict with 'SPI_CONTROLLER_MUST_TX' and 'SPI_3WIRE' mode,
i need to know the SPI_3WIRE direction,  currently i get this
information from 'struct spi_device'
and 'struct spi_transfer'
if ((spi_device->mode & SPI_3WIRE) && (spi_transfer->tx_buf == NULL)
&& (spi_transfer->rx_buf != NULL))
    this is a SPI_3WIRE_RX transfer
if ((spi_device->mode & SPI_3WIRE) && (spi_transfer->tx_buf != NULL)
&& (spi_transfer->rx_buf == NULL))
    this is a SPI_3WIRE_TX transfer

but, after spi-core create a dummy tx_buf or rx_buf, then i can't get
the correct spi_3wire direction.
actually, this dummy tx_buf is useless for SPI_3WIRE. it's has meaning
for SPI_SIMPLE_RX mode,
simulate SPI_FULL_DUMPLEX

how do you think?

thanks

best regards

Dillon