[PATCH V3 02/19] memory: tegra: Add MC flush support

[Thierry Reding]

On Mon, Jul 13, 2015 at 01:39:40PM +0100, Jon Hunter wrote:
> The Tegra memory controller implements a flush feature to flush pending
> accesses and prevent further accesses from occurring. This feature is
> used when powering down IP blocks to ensure the IP block is in a good
> state. The flushes are organised by software groups and IP blocks are
> assigned in hardware to the different software groups. Add helper
> functions for requesting a handle to an MC flush for a given
> software group and enabling/disabling the MC flush itself.
> 
> This is based upon a change by Vince Hsu <vinceh at nvidia.com>.
> 
> Signed-off-by: Jon Hunter <jonathanh at nvidia.com>
> ---
>  drivers/memory/tegra/mc.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++
>  drivers/memory/tegra/mc.h |   2 +
>  include/soc/tegra/mc.h    |  34 ++++++++++++++
>  3 files changed, 146 insertions(+)

Do we know if this is actually necessary? I remember having a discussion
with Arnd Bergmann a while ago, and the Linux driver model kind of
assumes that by the time a device is disabled all outstanding accesses
will have stopped.

Do we have a way to determine that this even makes a difference? Can we
trigger a case where not doing this would cause breakage and see that
adding this fixes that particular issue?

Thierry
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