Re: [patch 07/32] genirq/msi: Count the allocated MSI descriptors

Greg Kroah-Hartman
2021-11-27T12:21:16Z

On Sat, Nov 27, 2021 at 02:22:38AM +0100, Thomas Gleixner wrote:
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

No changelog?

Anyway, why do we care about the number of decriptors?

> ---
> include/linux/msi.h | 3 +++
> kernel/irq/msi.c | 18 ++++++++++++++++++
> 2 files changed, 21 insertions(+)
>
> --- a/include/linux/msi.h
> +++ b/include/linux/msi.h
> @@ -156,6 +156,7 @@ enum msi_desc_filter {
> * msi_device_data - MSI per device data
> * @lock: Spinlock to protect register access
> * @properties: MSI properties which are interesting to drivers
> + * @num_descs: The number of allocated MSI descriptors for the device
> * @attrs: Pointer to the sysfs attribute group
> * @platform_data: Platform-MSI specific data
> * @list: List of MSI descriptors associated to the device
> @@ -166,6 +167,7 @@ enum msi_desc_filter {
> struct msi_device_data {
> raw_spinlock_t lock;
> unsigned long properties;
> + unsigned int num_descs;
> const struct attribute_group **attrs;
> struct platform_msi_priv_data *platform_data;
> struct list_head list;
> @@ -208,6 +210,7 @@ static inline unsigned int msi_get_virq(
>
> void msi_lock_descs(struct device *dev);
> void msi_unlock_descs(struct device *dev);
> +unsigned int msi_device_num_descs(struct device *dev);
>
> struct msi_desc *__msi_first_desc(struct device *dev, enum msi_desc_filter filter, unsigned int base_index);
> struct msi_desc *msi_next_desc(struct device *dev);
> --- a/kernel/irq/msi.c
> +++ b/kernel/irq/msi.c
> @@ -82,6 +82,7 @@ int msi_add_msi_desc(struct device *dev,
> desc->pci = init_desc->pci;
>
> list_add_tail(&desc->list, &dev->msi.data->list);
> + dev->msi.data->num_descs++;
> return 0;
> }
>
> @@ -109,6 +110,7 @@ int msi_add_simple_msi_descs(struct devi
> list_add_tail(&desc->list, &list);
> }
> list_splice_tail(&list, &dev->msi.data->list);
> + dev->msi.data->num_descs += ndesc;
> return 0;
>
> fail:
> @@ -142,6 +144,7 @@ void msi_free_msi_descs_range(struct dev
> continue;
> list_del(&desc->list);
> free_msi_entry(desc);
> + dev->msi.data->num_descs--;
> }
> }
>
> @@ -157,6 +160,21 @@ bool msi_device_has_property(struct devi
> return !!(dev->msi.data->properties & prop);
> }
>
> +/**
> + * msi_device_num_descs - Query the number of allocated MSI descriptors of a device
> + * @dev: The device to read from
> + *
> + * Note: This is a lockless snapshot of msi_device_data::num_descs
> + *
> + * Returns the number of MSI descriptors which are allocated for @dev
> + */
> +unsigned int msi_device_num_descs(struct device *dev)
> +{
> + if (dev->msi.data)
> + return dev->msi.data->num_descs;

As this number can change after it is read, what will callers do with
it?

thanks,

greg k-h