linux-kernel - Re: [PATCH v1] powerpc/pci: restore LSI mappings on card present state change

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Message-ID: <4afe5232-78ae-42a0-9b6d-669cc7f6b051@linux.ibm.com>
Date: Thu, 29 Aug 2024 19:20:35 +0530
From: krishna kumar <krishnak@...ux.ibm.com>
To: Oleksandr Ocheretnyi <oocheret@...co.com>, xe-linux-external@...co.com,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Naveen N Rao <naveen@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sam Ravnborg <sam@...nborg.org>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] powerpc/pci: restore LSI mappings on card present
 state change


On 8/27/24 22:27, Oleksandr Ocheretnyi wrote:
> Commit 450be4960a0f ("powerpc/pci: Remove LSI mappings on device
> teardown") frees irq descriptors on PCIe hotplug link change event
> (Link Down), but the disposed mappings are not restored back on PCIe
> hotplug link change event (Card present).
>
> This change restores IRQ mappings disposed earlier when pcieport
> link's gone down. So, the call pci_read_irq_line is invoked again
> on pcieport's state change (Card present).

Few things are important to know regarding these change-sets:

1. The commit (450be4960aof) addressed an issue where the removal
or hot-unplug of an LSI passthroughed IO adapter was not working on
pseries machines. This was due to interrupt resources not getting cleaned
up before removal. Since there were no pcibios_* hooks for the interrupt
cleanup, the interrupt-related resource cleanup has been addressed using
the notifier framework and an explicit call of ppc_pci_intx_release().

2. Does without your current patch and after hot-plug operation, device is
not working (io not happening or interrupt not getting generated) correctly ?

3. There is already a pcibios_* hook available for creating the interrupt
mapping. Here's a snippet -

  /*
   * Called after device has been added to bus and
   * before sysfs has been created.
   */

void (*pcibios_bus_add_device)(struct pci_dev *pdev);

Above function calls - below function to restore the irq mapping.

/* Read default IRQs and fixup if necessary */
   pci_read_irq_line(dev);

4. Does the above pcibios_* hook not sufficient for enabling the interrupt
mapping or does it not getting invoked during hot-plug operation ?

>
> Fixes 450be4960a0f ("powerpc/pci: Remove LSI mappings on device teardown")
> Signed-off-by: Oleksandr Ocheretnyi <oocheret@...co.com>
> ---
>   arch/powerpc/kernel/pci-common.c | 30 ++++++++++++++++++++----------
>   1 file changed, 20 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index eac84d687b53..a0e7cab2baa7 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -390,22 +390,32 @@ static void ppc_pci_intx_release(struct kref *kref)
>   	kfree(vi);
>   }
>   
> +static int pci_read_irq_line(struct pci_dev *pci_dev);
> +
>   static int ppc_pci_unmap_irq_line(struct notifier_block *nb,
>   			       unsigned long action, void *data)
>   {
>   	struct pci_dev *pdev = to_pci_dev(data);
>   
> -	if (action == BUS_NOTIFY_DEL_DEVICE) {
> -		struct pci_intx_virq *vi;
> -
> -		mutex_lock(&intx_mutex);
> -		list_for_each_entry(vi, &intx_list, list_node) {
> -			if (vi->virq == pdev->irq) {
> -				kref_put(&vi->kref, ppc_pci_intx_release);
> -				break;
> +	switch (action) {
> +		case BUS_NOTIFY_DEL_DEVICE:
> +			{
> +				struct pci_intx_virq *vi;
> +
> +				mutex_lock(&intx_mutex);
> +				list_for_each_entry(vi, &intx_list, list_node) {
> +					if (vi->virq == pdev->irq) {
> +						kref_put(&vi->kref, ppc_pci_intx_release);
> +						break;
> +					}
> +				}
> +				mutex_unlock(&intx_mutex);
>   			}
> -		}
> -		mutex_unlock(&intx_mutex);
> +			break;
> +
> +		case BUS_NOTIFY_ADD_DEVICE:
> +			pci_read_irq_line(pdev);
> +			break;

The above code is fine only if my aforementioned points do not hold.

>   	}
>   
>   	return NOTIFY_DONE;


Best Regards,

Krishna