Re: [PATCH RFC 3/3] amba: bus: Move reading periphid operation from amba_match() to amba_probe()

[Zijun Hu]

On 2024/9/9 07:37, Zijun Hu wrote:
> From: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
> 
> amba_match(), as bus_type @amba_bustype's match(), reads periphid from
> hardware and may return -EPROBE_DEFER consequently, and it is the only
> one that breaks below ideal rule in current kernel tree:
> 
> bus_type's match() should only return bool type compatible integer 0 or
> 1 ideally since its main operations are lookup and comparison normally.
> 
> fixed by moving reading periphid operation to amba_probe().

or move to amba_dma_configure() which is the first bus_type's function
called after match()?

> 
> Signed-off-by: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
> ---
>  drivers/amba/bus.c       | 55 +++++++++++++++++++++++++++++-------------------
>  include/linux/amba/bus.h |  1 -
>  2 files changed, 33 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index 033d626aff46..8fe2e054b5ce 100644
> --- a/drivers/amba/bus.c
> +++ b/drivers/amba/bus.c
> @@ -188,7 +188,7 @@ static int amba_read_periphid(struct amba_device *dev)
>  	}
>  
>  	if (cid == AMBA_CID || cid == CORESIGHT_CID) {
> -		dev->periphid = pid;
> +		WRITE_ONCE(dev->periphid, pid);
>  		dev->cid = cid;
>  	}
>  
> @@ -246,24 +246,14 @@ static int amba_match(struct device *dev, const struct device_driver *drv)
>  	struct amba_device *pcdev = to_amba_device(dev);
>  	const struct amba_driver *pcdrv = to_amba_driver(drv);
>  
> -	mutex_lock(&pcdev->periphid_lock);
> -	if (!pcdev->periphid) {
> -		int ret = amba_read_periphid(pcdev);
> -
> -		/*
> -		 * Returning any error other than -EPROBE_DEFER from bus match
> -		 * can cause driver registration failure. So, if there's a
> -		 * permanent failure in reading pid and cid, simply map it to
> -		 * -EPROBE_DEFER.
> -		 */
> -		if (ret) {
> -			mutex_unlock(&pcdev->periphid_lock);
> -			return -EPROBE_DEFER;
> -		}
> -		dev_set_uevent_suppress(dev, false);
> -		kobject_uevent(&dev->kobj, KOBJ_ADD);
> -	}
> -	mutex_unlock(&pcdev->periphid_lock);
> +	/*
> +	 * For an AMBA device without valid periphid, only read periphid
> +	 * in amba_probe() for it when try to bind @amba_proxy_drv.
> +	 * For @pcdev->periphid, Reading here has a little race with
> +	 * writing in amba_probe().
> +	 */
> +	if (!READ_ONCE(pcdev->periphid))
> +		return pcdrv == &amba_proxy_drv ? 1 : 0;
>  
>  	/* When driver_override is set, only bind to the matching driver */
>  	if (pcdev->driver_override)
> @@ -315,10 +305,24 @@ static int amba_probe(struct device *dev)
>  {
>  	struct amba_device *pcdev = to_amba_device(dev);
>  	struct amba_driver *pcdrv = to_amba_driver(dev->driver);
> -	const struct amba_id *id = amba_lookup(pcdrv->id_table, pcdev);
> +	const struct amba_id *id;
>  	int ret;
>  
>  	do {
> +		if (!pcdev->periphid) {
> +			ret = amba_read_periphid(pcdev);
> +			if (ret) {
> +				dev_err_probe(dev, ret, "failed to read periphid\n");
> +			} else {
> +				dev_set_uevent_suppress(dev, false);
> +				kobject_uevent(&dev->kobj, KOBJ_ADD);
> +			}
> +
> +			ret = -EPROBE_DEFER;
> +			break;
> +		}
> +		id = amba_lookup(pcdrv->id_table, pcdev);
> +

or read periphid in this function later since it does some
preparation for hardware ready to read which also is done by
amba_read_periphid() ?

>  		ret = of_amba_device_decode_irq(pcdev);
>  		if (ret)
>  			break;
> @@ -389,10 +393,15 @@ static void amba_shutdown(struct device *dev)
>  
>  static int amba_dma_configure(struct device *dev)
>  {
> +	struct amba_device *pcdev = to_amba_device(dev);
>  	struct amba_driver *drv = to_amba_driver(dev->driver);
>  	enum dev_dma_attr attr;
>  	int ret = 0;
>  
> +	/* To successfully go to amba_probe() to read periphid */
> +	if (!pcdev->periphid)
> +		return 0;
> +
>  	if (dev->of_node) {
>  		ret = of_dma_configure(dev, dev->of_node, true);
>  	} else if (has_acpi_companion(dev)) {
> @@ -411,8 +420,12 @@ static int amba_dma_configure(struct device *dev)
>  
>  static void amba_dma_cleanup(struct device *dev)
>  {
> +	struct amba_device *pcdev = to_amba_device(dev);
>  	struct amba_driver *drv = to_amba_driver(dev->driver);
>  
> +	if (!pcdev->periphid)
> +		return;
> +
>  	if (!drv->driver_managed_dma)
>  		iommu_device_unuse_default_domain(dev);
>  }
> @@ -535,7 +548,6 @@ static void amba_device_release(struct device *dev)
>  	fwnode_handle_put(dev_fwnode(&d->dev));
>  	if (d->res.parent)
>  		release_resource(&d->res);
> -	mutex_destroy(&d->periphid_lock);
>  	kfree(d);
>  }
>  
> @@ -593,7 +605,6 @@ static void amba_device_initialize(struct amba_device *dev, const char *name)
>  	dev->dev.dma_mask = &dev->dev.coherent_dma_mask;
>  	dev->dev.dma_parms = &dev->dma_parms;
>  	dev->res.name = dev_name(&dev->dev);
> -	mutex_init(&dev->periphid_lock);
>  }
>  
>  /**
> diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
> index 958a55bcc708..4bb3467d9c3d 100644
> --- a/include/linux/amba/bus.h
> +++ b/include/linux/amba/bus.h
> @@ -67,7 +67,6 @@ struct amba_device {
>  	struct clk		*pclk;
>  	struct device_dma_parameters dma_parms;
>  	unsigned int		periphid;
> -	struct mutex		periphid_lock;
>  	unsigned int		cid;
>  	struct amba_cs_uci_id	uci;
>  	unsigned int		irq[AMBA_NR_IRQS];
>