Hi Marc,
On 20/02/18 20:25, Marc Zyngier wrote:
> Trying to do a kexec whilst the iommus are still on is proving to be
> a challenging exercise. It is terribly unsafe, as we're reusing the
> memory allocated for the page tables, leading to a likely crash.
>
> Let's implement a shutdown method that will at least try to stop
> DMA from going crazy behind our back. Note that we need to be
> extra cautious when doing so, as the IOMMU may not be clocked
> if controlled by a another master, as typical on Rockchip system.
Note that clock control is on the way[1], for pretty much that reason; I
think that series is more or less ready now.
> Suggested-by: Robin Murphy <robin.murphy at arm.com>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
> ---
> drivers/iommu/rockchip-iommu.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
> index 9d991c2d8767..6a3719e118da 100644
> --- a/drivers/iommu/rockchip-iommu.c
> +++ b/drivers/iommu/rockchip-iommu.c
> @@ -1209,6 +1209,23 @@ static int rk_iommu_remove(struct platform_device *pdev)
> return 0;
> }
>
> +static void rk_iommu_shutdown(struct platform_device *pdev)
> +{
> + struct rk_iommu *iommu = platform_get_drvdata(pdev);
> +
> + /*
> + * Be careful not to try to shutdown an otherwise unused
> + * IOMMU, as it is likely not to be clocked, and accessing it
> + * would just block. An IOMMU without a domain is likely to be
> + * unused, so let's use this as a (weak) guard.
> + */
Proper clock control will make this comment redundant, but IMO the check
remains valid either way - rk_iommu::domain being NULL means that no
devices are currently attached to an active domain, in which case
translation really should be disabled anyway.
Reviewed-by: Robin Murphy <robin.murphy at arm.com>
Thanks,
Robin.
[1]
https://www.mail-archive.com/linux-kernel at vger.kernel.org/msg1593978.html
> + if (iommu && iommu->domain) {
> + rk_iommu_enable_stall(iommu);
> + rk_iommu_disable_paging(iommu);
> + rk_iommu_force_reset(iommu);
> + }
> +}
> +
> static const struct of_device_id rk_iommu_dt_ids[] = {
> { .compatible = "rockchip,iommu" },
> { /* sentinel */ }
> @@ -1218,6 +1235,7 @@ MODULE_DEVICE_TABLE(of, rk_iommu_dt_ids);
> static struct platform_driver rk_iommu_driver = {
> .probe = rk_iommu_probe,
> .remove = rk_iommu_remove,
> + .shutdown = rk_iommu_shutdown,
> .driver = {
> .name = "rk_iommu",
> .of_match_table = rk_iommu_dt_ids,
>
