Re: [PATCH 4/4] Input: ads7846 - modificatons of _stop()/_disable() conditions

[Jason Wang <jason77.wang@gmail.com>]

Grazvydas Ignotas wrote:
> On Wed, Oct 13, 2010 at 6:12 AM, Jason Wang <jason77.wang@gmail.com> wrote:
>   
>> Hi Dmitry,
>>
>> I have validated the new patch based off the 2.6.36-rc7 on
>> the ti_omap3530evm, it works fine.
>>     
>
> Working here on pandora too, applied on top of linux-next (did not
> test suspend though).
>
> Not caused by this patch, but the old problem where lower measurement
> bits get lost is back - when I draw diagonal line it looks like
> stairs. I think it's caused by OMAP SPI driver, CCing linux-omap.
>
>   
Yes, it is OMAP spi driver issues, I have met the same problem before, 
please refer to:
http://www.spinics.net/lists/arm-kernel/msg91538.html

you can apply this patch and test again.



 From 393f445ab899abaf5d60a55a54f242c430507047 Mon Sep 17 00:00:00 2001
From: Jason Wang <jason77.wang@gmail.com>
Date: Thu, 14 Oct 2010 10:08:07 +0800
Subject: [PATCH] spi/omap2_mcspi: disable channel after TX_ONLY transfer 
in PIO mode

In TX_ONLY transfer, the SPI controller can also receive data
simultaneously and saves them in rx register. After the TX_ONLY
transfer, the rx register will hold random data received during
last tx transaction.

If the next transfer is RX_ONLY, this random data has
the possibility to affect this transfer like this:

  If the spi controller is changed from TX_ONLY to RX_ONLY mode,
  The random data makes the rx register full imediately and
  triggers a dummy write (in SPI RX_ONLY transfer, we need a dummy
  write to trigger the first transaction).

  So the first data received in RX_ONLY transfer will be that
  random data instead of something meaningfug.

We can avoid this by a Disable/reenable toggle of the spi channel
after the TX_ONLY transfer, since it purges the rx register.

Signed-off-by: Jason Wang <jason77.wang@gmail.com>
---
 drivers/spi/omap2_mcspi.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/spi/omap2_mcspi.c b/drivers/spi/omap2_mcspi.c
index b3a94ca..43fab41 100644
--- a/drivers/spi/omap2_mcspi.c
+++ b/drivers/spi/omap2_mcspi.c
@@ -644,6 +644,12 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct 
spi_transfer *xfer)
                } else if (mcspi_wait_for_reg_bit(chstat_reg,
                                OMAP2_MCSPI_CHSTAT_EOT) < 0)
                        dev_err(&spi->dev, "EOT timed out\n");
+
+               /* disable chan to purge rx datas received in TX_ONLY 
transfer,
+                * otherwise these rx datas will affect the direct following
+                * RX_ONLY transfer.
+                */
+               omap2_mcspi_set_enable(spi, 0);
        }
 out:
        omap2_mcspi_set_enable(spi, 1);
-- 
1.5.6.5