linux-kernel - Re: [PATCH] spi: spi-bcm2835.c: Fix 3-wire mode

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Date:   Fri, 28 Jun 2019 17:23:54 +0200
From:   Stefan Wahren <wahrenst@....net>
To:     Nuno Sá <nuno.sa@...log.com>, broonie@...nel.org,
        eric@...olt.net, Martin Sperl <kernel@...tin.sperl.org>,
        Lukas Wunner <lukas@...ner.de>
Cc:     f.fainelli@...il.com, rjui@...adcom.com, sbranden@...adcom.com,
        linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH] spi: spi-bcm2835.c: Fix 3-wire mode

Hi Nuno,

Am 28.06.19 um 14:30 schrieb Nuno Sá:
> As stated in
> https://www.raspberrypi.org/documentation/hardware/raspberrypi/spi/README.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 Sá <nuno.sa@...log.com>

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

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