Re: [PATCH 2/11] memory: tegra: add mc flush support

[Thierry Reding <thierry.reding@gmail.com>]

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On Tue, Dec 23, 2014 at 06:39:55PM +0800, Vince Hsu wrote:
> The flush operation of memory clients is needed for various IP blocks in
> the Tegra SoCs to perform a clean reset.
> 
> Signed-off-by: Vince Hsu <vinceh@nvidia.com>
> ---
>  drivers/memory/tegra/mc.c | 21 +++++++++++++++++++++
>  include/soc/tegra/mc.h    | 23 ++++++++++++++++++++++-
>  2 files changed, 43 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/memory/tegra/mc.c b/drivers/memory/tegra/mc.c
> index fe3c44e7e1d1..a2928b4b26fe 100644
> --- a/drivers/memory/tegra/mc.c
> +++ b/drivers/memory/tegra/mc.c
> @@ -62,6 +62,27 @@ static const struct of_device_id tegra_mc_of_match[] = {
>  };
>  MODULE_DEVICE_TABLE(of, tegra_mc_of_match);
>  
> +int tegra_mc_flush(struct tegra_mc *mc, unsigned int swgroup, bool enable)
> +{
> +	int i;
> +	const struct tegra_mc_hr *client;
> +
> +	if (!mc || !mc->soc->hr_clients ||
> +			!mc->soc->ops || !mc->soc->ops->flush)
> +		return -EINVAL;;
> +
> +	client = mc->soc->hr_clients;
> +
> +	for (i = 0; i < mc->soc->num_hr_clients; i++, client++) {
> +		if (swgroup == client->swgroup) {
> +			return mc->soc->ops->flush(mc, client, enable);
> +		}
> +	}
> +
> +	return -EINVAL;
> +}
> +EXPORT_SYMBOL(tegra_mc_flush);

Like Lucas already mentioned in response to another patch, having a
boolean "enable" argument is suboptimal here. Now according to
documentation the proper reset sequence for clients is something like
this:

	1) set the FLUSH_ENABLE bit for the client
	2) poll the FLUSH_DONE bit for the client
	3) assert reset to the client using the CAR
	4) deassert reset to the client using the CAR
	5) clear the FLUSH_ENABLE bit for the client

This is really inconvenient because we can't flush the client using a
single operation. So I think we'll need two functions here, something
like: tegra_mc_flush_enable/disable(), or tegra_mc_flush_{,de}assert().
Or maybe even: tegra_mc_reset_{,de}assert() to mirror the reset
controller API. I suppose we could even export it using the reset
controller framework.

Doing so would allow us to have power domain DT nodes like this:

	pmc@0,7000e400 {
		power-domains {
			...

			gpu {
				resets = <&tegra_car 184>,
					 <&mc TEGRA_SWGROUP_GPU>;
				reset-names = "module", "client";
			};

			...
		};
	};

The PMC driver could then grab the "module" and "client" resets and do
something like this:

	reset_control_assert(powergate->rst_client);
	reset_control_assert(powergate->rst_module);
	reset_control_deassert(powergate->rst_module);
	reset_control_deassert(powergate->rst_client);

Optionally the above could be extended with a reset_control_status()-
loop. Alternatively reset_control_assert() would block until the
FLUSH_DONE bit is set.

Stephen, Peter, any thoughts on the above?

Thierry

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