Applied "spi: pxa2xx: Deal with the leftover garbage in TXFIFO" to the spi tree

[Mark Brown <broonie@xxxxxxxxxx>]

The patch

   spi: pxa2xx: Deal with the leftover garbage in TXFIFO

has been applied to the spi tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 82391856191878bb0047259817ab32f88438aa33 Mon Sep 17 00:00:00 2001
From: Lubomir Rintel <lkundrak@xxxxx>
Date: Tue, 13 Nov 2018 11:22:28 +0100
Subject: [PATCH] spi: pxa2xx: Deal with the leftover garbage in TXFIFO

There doesn't seem to be a way to empty TXFIFO on MMP2. The datasheet is
super-secret and the method described in Armada 16x manual won't work:

  "The TXFIFO and RXFIFO are cleared to 0b0 when the SSPx port is reset or
  disabled (by writing a 0b0 to the <Synchronous Serial Port Enable> field
  in the SSP Control Register 0)."

  # devmem 0xd4037008           # read SSSR
  0x0000F204
  # devmem 0xd4037000 32 0x07   # SSE off in SSCR0
  # devmem 0xd4037000 32 0x87   # SSE on
  # devmem 0xd4037008
  0x0000F204
         ^ TXFIFO level is still 2. Sigh.

The OLPC 1.75 boot firmware leaves two bytes in the TXFIFO. Those are
basically throwaway bytes used in response to the messages from the EC.
The OLPC kernel copes with this by power-cycling the hardware. Perhaps
the firmware should do this instead.

Other than that, there's not much we can do other than complain loudly
until the garbage gets drained and discard the actual data... For the
OLPC EC this will work just fine and pushing more data to TXFIFO would
break further transactions.

Signed-off-by: Lubomir Rintel <lkundrak@xxxxx>
Acked-by: Pavel Machek <pavel@xxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 drivers/spi/spi-pxa2xx.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
index 69b221e34b2d..e6a606354f62 100644
--- a/drivers/spi/spi-pxa2xx.c
+++ b/drivers/spi/spi-pxa2xx.c
@@ -1078,6 +1078,20 @@ static int pxa2xx_spi_transfer_one(struct spi_controller *master,
 			pxa2xx_spi_write(drv_data, SSTO, chip->timeout);
 	}
 
+	if (drv_data->ssp_type == MMP2_SSP) {
+		u8 tx_level = (pxa2xx_spi_read(drv_data, SSSR)
+					& SSSR_TFL_MASK) >> 8;
+
+		if (tx_level) {
+			/* On MMP2, flipping SSE doesn't to empty TXFIFO. */
+			dev_warn(&spi->dev, "%d bytes of garbage in TXFIFO!\n",
+								tx_level);
+			if (tx_level > transfer->len)
+				tx_level = transfer->len;
+			drv_data->tx += tx_level;
+		}
+	}
+
 	if (spi_controller_is_slave(master)) {
 		while (drv_data->write(drv_data))
 			;
-- 
2.19.1