[PATCH 3/3] ramips: add RT6855A SoC Linux support patches

[Chuanhong Guo]

On Thu, Dec 24, 2020 at 12:52 AM Rafaël Carré <funman at videolan.org> wrote:
> diff --git a/target/linux/ramips/patches-5.4/304-HACK-spi-mt7621-rt6855a-fix.patch b/target/linux/ramips/patches-5.4/304-HACK-spi-mt7621-rt6855a-fix.patch
> new file mode 100644
> index 0000000000..972e969fc4
> --- /dev/null
> +++ b/target/linux/ramips/patches-5.4/304-HACK-spi-mt7621-rt6855a-fix.patch
> @@ -0,0 +1,35 @@
> +From cbc220c515f2b387462795b730b52dea96687885 Mon Sep 17 00:00:00 2001
> +From: =?UTF-8?q?Rafa=C3=ABl=20Carr=C3=A9?= <funman at videolan.org>
> +Date: Wed, 23 Dec 2020 14:18:31 +0100
> +Subject: [PATCH 2/5] HACK: spi-mt7621: rt6855a fix
> +MIME-Version: 1.0
> +Content-Type: text/plain; charset=UTF-8
> +Content-Transfer-Encoding: 8bit
> +
> +TODO: no idea what this does or if it's needed on other targets
> +using this driver.

This spi controller doesn't provide us with chipselect control, so
the maximum transfer size is limited to the buffer size of
MOREBUF mode.
In order to get rid of that limit, we need to hold chipselect pins
ourselves. It's accomplished in spi-mt7621.c this way:
1. set RS_SLAVE_SEL to 7 so that controller controls
    nonexistent CS7 for every transfer.
2. set actual chipselect pins by configuring CS polarity
    in SPI_CS_POLAR register.
Now we can trigger the controller to do multiple transfers
without deactivating chipselects in between, thus the
transfer size limit is lifted for this controller.

Datasheet for MT7688 is publicly available:
https://labs.mediatek.com/en/download/50WkbgbH
and you can find register details there.

> +
> +Signed-off-by: Rafaël Carré <funman at videolan.org>
> +---
> + drivers/spi/spi-mt7621.c | 5 ++++-
> + 1 file changed, 4 insertions(+), 1 deletion(-)
> +
> +diff --git a/drivers/spi/spi-mt7621.c b/drivers/spi/spi-mt7621.c
> +index 2c3b7a2a1ec7..58fb028ed776 100644
> +--- a/drivers/spi/spi-mt7621.c
> ++++ b/drivers/spi/spi-mt7621.c
> +@@ -87,7 +87,10 @@ static void mt7621_spi_set_cs(struct spi_device *spi, int enable)
> +        * reliably)
> +        */
> +       master = mt7621_spi_read(rs, MT7621_SPI_MASTER);
> +-      master |= MASTER_RS_SLAVE_SEL | MASTER_MORE_BUFMODE;
> ++      master |= MASTER_MORE_BUFMODE;
> ++#ifndef CONFIG_SOC_RT6855A
> ++      master |= MASTER_RS_SLAVE_SEL;
> ++#endif
> +       master &= ~MASTER_FULL_DUPLEX;
> +       mt7621_spi_write(rs, MT7621_SPI_MASTER, master);
> +
> +--
> +2.27.0
> +

-- 
Regards,
Chuanhong Guo