linux-kernel - Re: [PATCH v5] iommu/tegra-smmu: Add pagetable mappings to debugfs

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Message-ID: <acad1a15-b4ad-e74e-647e-d50d15d8d3d1@gmail.com>
Date:   Wed, 17 Mar 2021 02:43:00 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>, joro@...tes.org,
        thierry.reding@...il.com, will@...nel.org
Cc:     vdumpa@...dia.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] iommu/tegra-smmu: Add pagetable mappings to debugfs

15.03.2021 23:36, Nicolin Chen пишет:
> +static int tegra_smmu_mappings_show(struct seq_file *s, void *data)
> +{
> +	struct tegra_smmu_group_debug *group_debug = s->private;
> +	const struct tegra_smmu_swgroup *group;
> +	struct tegra_smmu_as *as;
> +	struct tegra_smmu *smmu;
> +	unsigned int pd_index;
> +	unsigned int pt_index;
> +	unsigned long flags;
> +	u64 pte_count = 0;
> +	u32 pde_count = 0;
> +	u32 val, ptb_reg;
> +	u32 *pd;
> +
> +	if (!group_debug || !group_debug->priv || !group_debug->group)
> +		return 0;

I'm also now curious how difficult would be to read out the actual h/w
state, i.e. check whether ASID is enabled and then dynamically map the
pointed pages instead of using pages allocated by driver. This will show
us the real h/w state. For example this may show mappings left after
bootloader or after reboot/kexec, which could be handy to see.