linux-kernel - Re: [PATCH 3/5] iommu/tegra-smmu: Use iommu_fwspec in .probe_/.attach

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Message-ID: <20200928072955.GE2837573@ulmo>
Date:   Mon, 28 Sep 2020 09:29:55 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Nicolin Chen <nicoleotsuka@...il.com>, joro@...tes.org,
        krzk@...nel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        jonathanh@...dia.com
Subject: Re: [PATCH 3/5] iommu/tegra-smmu: Use iommu_fwspec in
 .probe_/.attach_device()

On Sat, Sep 26, 2020 at 05:48:17PM +0300, Dmitry Osipenko wrote:
> 26.09.2020 11:07, Nicolin Chen пишет:
> ...
> > +	/* NULL smmu pointer means that SMMU driver is not probed yet */
> > +	if (unlikely(!smmu))
> > +		return ERR_PTR(-EPROBE_DEFER);
> 
> Hello, Nicolin!
> 
> Please don't pollute code with likely/unlikely. This is not a
> performance-critical code.
> 
> ...
> > -static struct platform_driver tegra_mc_driver = {
> > +struct platform_driver tegra_mc_driver = {
> >  	.driver = {
> >  		.name = "tegra-mc",
> >  		.of_match_table = tegra_mc_of_match,
> > diff --git a/include/soc/tegra/mc.h b/include/soc/tegra/mc.h
> > index 1238e35653d1..49a4cf64c4b9 100644
> > --- a/include/soc/tegra/mc.h
> > +++ b/include/soc/tegra/mc.h
> > @@ -184,4 +184,6 @@ struct tegra_mc {
> >  int tegra_mc_write_emem_configuration(struct tegra_mc *mc, unsigned long rate);
> >  unsigned int tegra_mc_get_emem_device_count(struct tegra_mc *mc);
> >  
> > +extern struct platform_driver tegra_mc_driver;
> 
> No global variables, please. See for the example:
> 
> https://elixir.bootlin.com/linux/v5.9-rc6/source/drivers/devfreq/tegra20-devfreq.c#L100
> 
> The tegra_get_memory_controller() is now needed by multiple Tegra
> drivers, I think it should be good to have it added into the MC driver
> and then make it globally available for all drivers by making use of
> of_find_matching_node_and_match().
> 
> diff --git a/drivers/memory/tegra/mc.c b/drivers/memory/tegra/mc.c
> index e1db209fd2ea..ed1bd6d00aaf 100644
> --- a/drivers/memory/tegra/mc.c
> +++ b/drivers/memory/tegra/mc.c
> @@ -43,6 +43,29 @@ static const struct of_device_id tegra_mc_of_match[] = {
>  };
>  MODULE_DEVICE_TABLE(of, tegra_mc_of_match);
> 
> +struct tegra_mc *tegra_get_memory_controller(void)
> +{
> +	struct platform_device *pdev;
> +	struct device_node *np;
> +	struct tegra_mc *mc;
> +
> +	np = of_find_matching_node_and_match(NULL, tegra_mc_of_match, NULL);
> +	if (!np)
> +		return ERR_PTR(-ENOENT);
> +
> +	pdev = of_find_device_by_node(np);
> +	of_node_put(np);
> +	if (!pdev)
> +		return ERR_PTR(-ENODEV);
> +
> +	mc = platform_get_drvdata(pdev);
> +	if (!mc)
> +		return ERR_PTR(-EPROBE_DEFER);
> +
> +	return mc;
> +}
> +EXPORT_SYMBOL_GPL(tegra_get_memory_controller);

We already have tegra_smmu_find(), which should be enough for this
particular use-case.

Thierry

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