Re: linux 4.2-rc1 broken Nokia N900

[Sebastian Reichel <sre@kernel.org>]

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Hi,

On Tue, Jul 21, 2015 at 07:17:41PM -0500, Michael Welling wrote:
> On Tue, Jul 21, 2015 at 11:34:41AM +0200, Pavel Machek wrote:
> 
> This code has my head spinning.
> 
> I found that the errors do not occur when the driver is built into the kernel.
> 
> I also found that with the patch below the errors go away.
> 
> Not sure if it is acceptible but see if it fixes things on your side.
> 
> 
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index cf8b91b..3164d13 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -1801,11 +1801,11 @@ int spi_setup(struct spi_device *spi)
>  	if (!spi->max_speed_hz)
>  		spi->max_speed_hz = spi->master->max_speed_hz;
>  
> -	spi_set_cs(spi, false);
> -
>  	if (spi->master->setup)
>  		status = spi->master->setup(spi);
>  
> +	spi_set_cs(spi, false);
> +
>  	dev_dbg(&spi->dev, "setup mode %d, %s%s%s%s%u bits/w, %u Hz max --> %d\n",
>  			(int) (spi->mode & (SPI_CPOL | SPI_CPHA)),
>  			(spi->mode & SPI_CS_HIGH) ? "cs_high, " : "",

mh. maybe a runtime PM issue?

 * external abort on non-linefetch: address cannot be accessed,
   since the module's clocks are disabled
 * built-in works, module not: built-in is probably a little bit
   faster (module must not be loaded from filesystem), so that
   the device has not yet been suspended
 * Before 4.2, omap2_mcspi_set_cs() was called in the setup
   routine, which acquired runtime PM
 * In 4.2, omap2_mcspi_set_cs() seems to be called without a
   prior pm_runtime_get_sync()
 * With your workaround, the device has not yet returned to
   suspend after the runtime PM acquisition in setup()

So I suggest trying the following (compile tested only) patch:

-- Sebastian

diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c
index 5867384..f7d9ffd 100644
--- a/drivers/spi/spi-omap2-mcspi.c
+++ b/drivers/spi/spi-omap2-mcspi.c
@@ -245,6 +245,7 @@ static void omap2_mcspi_set_enable(const struct spi_device *spi, int enable)
 
 static void omap2_mcspi_set_cs(struct spi_device *spi, bool enable)
 {
+       struct omap2_mcspi *mcspi = spi_master_get_devdata(spi->master);
        u32 l;
 
        /* The controller handles the inverted chip selects
@@ -255,6 +256,8 @@ static void omap2_mcspi_set_cs(struct spi_device *spi, bool enable)
                enable = !enable;
 
        if (spi->controller_state) {
+               pm_runtime_get_sync(mcspi->dev);
+
                l = mcspi_cached_chconf0(spi);
 
                if (enable)
@@ -263,6 +266,9 @@ static void omap2_mcspi_set_cs(struct spi_device *spi, bool enable)
                        l |= OMAP2_MCSPI_CHCONF_FORCE;
 
                mcspi_write_chconf0(spi, l);
+
+               pm_runtime_mark_last_busy(mcspi->dev);
+               pm_runtime_put_autosuspend(mcspi->dev);
        }
 }
 

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