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

[Georgi Djakov]

On 18.11.20 0:02, Dmitry Osipenko wrote:
> 17.11.2020 23:24, Georgi Djakov пишет:
> > 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@xxxxxxxxx>
> > > Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > > ---
> > >    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!
>
> Hello Georgi,
>
> Returning zeros doesn't allow us to skip the initialization that is done
> by provider->set(node, node) in icc_node_add(). It will reconfigure
> memory latency in accordance to a zero memory bandwidth, which is wrong
> to do.
>
> It actually should be more preferred to preset bandwidth to a maximum
> before all drivers are synced, but this should be done only once we will
> wire up all drivers to use ICC framework. For now it's safer to keep the
> default hardware configuration untouched.

Ok, thanks for clarifying! Is there a way to read this hardware 
configuration and convert it to initial bandwidth? That's the
idea of the get_bw() callback actually. I am just curious and
trying to get a better understanding how this works and if it
would be useful for Tegra.

Thanks,
Georgi