Re: [PATCH 3/3] soc/tegra: pmc: Don't create fake interrupt hierarchy levels

Thierry Reding
2020-10-05T11:33:40Z

[-- Attachment #1: Type: text/plain, Size: 2617 bytes --]

On Mon, Oct 05, 2020 at 12:14:43PM +0100, Marc Zyngier wrote:
> The Tegra PMC driver does ungodly things with the interrupt hierarchy,
> repeatedly corrupting it by pulling hwirq numbers out of thin air,
> overriding existing IRQ mappings and changing the handling flow
> of unsuspecting users.
>
> All of this is done in the name of preserving the interrupt hierarchy
> even when these levels do not exist in the HW. Together with the use
> of proper IRQs for IPIs, this leads to an unbootable system as the
> rescheduling IPI gets repeatedly repurposed for random drivers...
>
> Instead, let's allow the hierarchy to be trimmed to the level that
> actually makes sense for the HW, and not any deeper. This avoids
> having unnecessary callbacks, overriding mappings, and otherwise
> keeps the hierarchy sane.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> drivers/soc/tegra/pmc.c | 79 +++++++++++++++--------------------------
> 1 file changed, 29 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
> index 9960f7c18431..4eea3134fb3e 100644
> --- a/drivers/soc/tegra/pmc.c
> +++ b/drivers/soc/tegra/pmc.c
> @@ -1993,6 +1993,30 @@ static int tegra_pmc_irq_translate(struct irq_domain *domain,
> return 0;
> }
>
> +/* Trim the irq hierarchy from a particular irq domain */
> +static void trim_hierarchy(unsigned int virq, struct irq_domain *domain)
> +{
> + struct irq_data *tail, *irq_data = irq_get_irq_data(virq);
> +
> + /* The PMC doesn't generate any interrupt by itself */
> + if (WARN_ON(!irq_data->parent_data))
> + return;
> +
> + /* Skip until we find the right domain */
> + while (irq_data->parent_data && irq_data->parent_data->domain != domain)
> + irq_data = irq_data->parent_data;
> +
> + /* Sever the inner part of the hierarchy... */
> + tail = irq_data->parent_data;
> + irq_data->parent_data = NULL;
> +
> + /* ... and free it */
> + for (irq_data = tail; irq_data; irq_data = tail) {
> + tail = irq_data->parent_data;
> + kfree(irq_data);
> + };
> +}

That kind of looks like what I originally wanted to do and (naively)
thought that passing the (0, NULL, NULL) triplet would achieve.

Given that this is fairly low-level stuff that deals with the inner
workings of the IRQ infrastructure, should we eventually pull this out
of the driver and make it into a core helper? I don't seriously expect
this to be widely useful, but putting it into the core might help keep
it more maintainable.

I volunteer to do that work if you think it's a good idea.

Thierry

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]