linux-kernel - Re: [PATCH v9 01/17] memory: tegra30: Support interconnect framework

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Date:   Tue, 17 Nov 2020 22:24:37 +0200
From:   Georgi Djakov <georgi.djakov@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Mikko Perttunen <cyndis@...si.fi>,
        Viresh Kumar <vireshk@...nel.org>,
        Peter Geis <pgwipeout@...il.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Cc:     linux-tegra@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v9 01/17] memory: tegra30: Support interconnect framework

Hi Dmitry,

Thank you working on this!

On 15.11.20 23:29, Dmitry Osipenko wrote:
> Now Internal and External memory controllers are memory interconnection
> providers. This allows us to use interconnect API for tuning of memory
> configuration. EMC driver now supports OPPs and DVFS. MC driver now
> supports tuning of memory arbitration latency, which needs to be done
> for ISO memory clients, like a Display client for example.
> 
> Tested-by: Peter Geis <pgwipeout@...il.com>
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>   drivers/memory/tegra/Kconfig       |   1 +
>   drivers/memory/tegra/tegra30-emc.c | 349 +++++++++++++++++++++++++++--
>   drivers/memory/tegra/tegra30.c     | 173 +++++++++++++-
>   3 files changed, 501 insertions(+), 22 deletions(-)
> 
[..]> diff --git a/drivers/memory/tegra/tegra30.c 
b/drivers/memory/tegra/tegra30.c
> index d0314f29608d..ea849003014b 100644
> --- a/drivers/memory/tegra/tegra30.c
> +++ b/drivers/memory/tegra/tegra30.c
[..]
> +
> +static int tegra30_mc_icc_set(struct icc_node *src, struct icc_node *dst)
> +{
> +	struct tegra_mc *mc = icc_provider_to_tegra_mc(src->provider);
> +	const struct tegra_mc_client *client = &mc->soc->clients[src->id];
> +	u64 peak_bandwidth = icc_units_to_bps(src->peak_bw);
> +
> +	/*
> +	 * Skip pre-initialization that is done by icc_node_add(), which sets
> +	 * bandwidth to maximum for all clients before drivers are loaded.
> +	 *
> +	 * This doesn't make sense for us because we don't have drivers for all
> +	 * clients and it's okay to keep configuration left from bootloader
> +	 * during boot, at least for today.
> +	 */
> +	if (src == dst)
> +		return 0;

Nit: The "proper" way to express this should be to implement the
.get_bw() callback to return zero as initial average/peak bandwidth.
I'm wondering if this will work here?

The rest looks good to me!

Thanks,
Georgi