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Subject: Re: [PATCH] spi: spi-bcm2835.c: Fix 3-wire mode
To:     =?UTF-8?Q?Nuno_S=c3=a1?= <nuno.sa@analog.com>, broonie@kernel.org,
        eric@anholt.net, Martin Sperl <kernel@martin.sperl.org>,
        Lukas Wunner <lukas@wunner.de>
Cc:     f.fainelli@gmail.com, rjui@broadcom.com, sbranden@broadcom.com,
        linux-kernel@vger.kernel.org,
        bcm-kernel-feedback-list@broadcom.com,
        linux-rpi-kernel@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-spi@vger.kernel.org
References: <20190628123023.4696-1-nuno.sa@analog.com>
From:   Stefan Wahren <wahrenst@gmx.net>
Message-ID: <1b932c61-982b-aae0-1fef-3c574e7d17eb@gmx.net>
Date:   Fri, 28 Jun 2019 17:23:54 +0200
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Hi Nuno,

Am 28.06.19 um 14:30 schrieb Nuno S=C3=A1:
> As stated in
> https://www.raspberrypi.org/documentation/hardware/raspberrypi/spi/READM=
E.md,
> one of rx or tx buffer's must be null. However, if DMA is enabled, the
> driver sets the SPI_CONTROLLER_MUST_RX | SPI_CONTROLLER_MUST_TX on the
> controller flags. Hence, the spi core will provide dummy buffers even if
> one of the buffers was set to null by the device driver. Thus, the
> communication with the 3-wire device fails.
>
> This patch uses the prepare_message callback to look for the device mode
> and sets/clears the SPI_CONTROLLER_MUST_RX | SPI_CONTROLLER_MUST_TX on a
> per spi message basis. It also assumes that DMA is not supported on
> half-duplex devices.
>
> Signed-off-by: Nuno S=C3=A1 <nuno.sa@analog.com>

i never tested the 3-wire mode. Could you please describe your test setup?

@Martin, @Lukas Are you fine with this patch?