RE: [PATCH V5 05/12] drivers: platform: Configure dma operations at probe time

["Sricharan" <sricharan-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

Hi Robin,

>On 19/01/17 15:05, Sricharan R wrote:
>> Configuring DMA ops at probe time will allow deferring device probe when
>> the IOMMU isn't available yet. The dma_configure for the device is
>> now called from the generic device_attach callback just before the
>> bus/driver probe is called. This way, configuring the DMA ops for the
>> device would be called at the same place for all bus_types, hence the
>> deferred probing mechanism should work for all buses as well.
>>
>> pci_bus_add_devices    (platform/amba)(_device_create/driver_register)
>>        |                         |
>> pci_bus_add_device     (device_add/driver_register)
>>        |                         |
>> device_attach           device_initial_probe
>>        |                         |
>> __device_attach_driver    __device_attach_driver
>>        |
>> driver_probe_device
>>        |
>> really_probe
>>        |
>> dma_configure
>>
>> Similarly on the device/driver_unregister path __device_release_driver is
>> called which inturn calls dma_deconfigure.
>>
>> Signed-off-by: Sricharan R <sricharan@codeaurora.org>
>> ---
>>  * Removed the dma configuration for the pci devices in case of DT
>>    from pci_dma_configure which was hanging outside separately and
>>    doing it in dma_configure function itself.
>>
>>  drivers/base/dd.c           |  9 +++++++++
>>  drivers/base/dma-mapping.c  | 32 ++++++++++++++++++++++++++++++++
>>  drivers/of/platform.c       |  5 +----
>>  drivers/pci/probe.c         |  5 +----
>>  include/linux/dma-mapping.h |  3 +++
>>  5 files changed, 46 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>> index a1fbf55..4882f06 100644
>> --- a/drivers/base/dd.c
>> +++ b/drivers/base/dd.c
>> @@ -19,6 +19,7 @@
>>
>>  #include <linux/device.h>
>>  #include <linux/delay.h>
>> +#include <linux/dma-mapping.h>
>>  #include <linux/module.h>
>>  #include <linux/kthread.h>
>>  #include <linux/wait.h>
>> @@ -356,6 +357,10 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>>  	if (ret)
>>  		goto pinctrl_bind_failed;
>>
>> +	ret = dma_configure(dev);
>> +	if (ret)
>> +		goto dma_failed;
>> +
>>  	if (driver_sysfs_add(dev)) {
>>  		printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
>>  			__func__, dev_name(dev));
>> @@ -417,6 +422,8 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>>  	goto done;
>>
>>  probe_failed:
>> +	dma_deconfigure(dev);
>> +dma_failed:
>>  	if (dev->bus)
>>  		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
>>  					     BUS_NOTIFY_DRIVER_NOT_BOUND, dev);
>> @@ -826,6 +833,8 @@ static void __device_release_driver(struct device *dev, struct device *parent)
>>  			drv->remove(dev);
>>
>>  		device_links_driver_cleanup(dev);
>> +		dma_deconfigure(dev);
>> +
>>  		devres_release_all(dev);
>>  		dev->driver = NULL;
>>  		dev_set_drvdata(dev, NULL);
>> diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
>> index efd71cf..dfe6fd7 100644
>> --- a/drivers/base/dma-mapping.c
>> +++ b/drivers/base/dma-mapping.c
>> @@ -10,6 +10,7 @@
>>  #include <linux/dma-mapping.h>
>>  #include <linux/export.h>
>>  #include <linux/gfp.h>
>> +#include <linux/of_device.h>
>>  #include <linux/slab.h>
>>  #include <linux/vmalloc.h>
>>
>> @@ -341,3 +342,34 @@ void dma_common_free_remap(void *cpu_addr, size_t size, unsigned long vm_flags)
>>  	vunmap(cpu_addr);
>>  }
>>  #endif
>> +
>> +/*
>> + * Common configuration to enable DMA API use for a device
>> + */
>> +#include <linux/pci.h>
>> +
>> +int dma_configure(struct device *dev)
>> +{
>> +	struct device *_dev = dev;
>> +	int is_pci = dev_is_pci(dev);
>> +
>> +	if (is_pci) {
>> +		_dev = pci_get_host_bridge_device(to_pci_dev(dev));
>> +		if (IS_ENABLED(CONFIG_OF) && _dev->parent &&
>> +		    _dev->parent->of_node)
>> +			_dev = _dev->parent;
>> +	}
>> +
>> +	if (_dev->of_node)
>> +		of_dma_configure(dev, _dev->of_node);
>> +
>> +	if (is_pci)
>> +		pci_put_host_bridge_device(_dev);
>
>There's a fun bug here - at this point _dev is the *parent* of the
>bridge device, so we put the refcount on the wrong device (the platform
>device representing the host controller, rather than the PCI device
>representing its insides), which frees the guy we're in the middle of
>probing, and things rapidly go wrong afterwards:
>

ha my bad, right. I will change to fix this. I was testing this with a couple
of pci devices, but it did not show up. Thanks for pointing this out.
I will borrow the variable names from the hunk below. 

>[    1.461026] bus: 'platform': driver_probe_device: matched device
>40000000.pcie-controller with driver pci-host-generic
>[    1.471640] bus: 'platform': really_probe: probing driver
>pci-host-generic with device 40000000.pcie-controller
>[    1.481678] OF: PCI: host bridge /pcie-controller@40000000 ranges:
>
>...
>
>[    2.158259] bus: 'pci': driver_probe_device: matched device
>0000:02:10.0 with driver pcieport
>[    2.166716] bus: 'pci': really_probe: probing driver pcieport with
>device 0000:02:10.0
>[    2.174590] pci 0000:02:10.0: Driver pcieport requests probe deferral
>[    2.180978] pci 0000:02:10.0: Added to deferred list
>[    2.185915] bus: 'pci': driver_probe_device: matched device
>0000:02:1f.0 with driver pcieport
>[    2.194366] bus: 'pci': really_probe: probing driver pcieport with
>device 0000:02:1f.0
>[    2.202237] pci 0000:02:1f.0: Driver pcieport requests probe deferral
>[    2.208625] pci 0000:02:1f.0: Added to deferred list
>[    2.213582] driver: 'pci-host-generic': driver_bound: bound to device
>'���v����.pcie-controller'
>[    2.222293] bus: 'platform': really_probe: bound device
>���v����.pcie-controller to driver pci-host-generic
>[    2.232041] Unable to handle kernel NULL pointer dereference at
>virtual address 00000000
>
>I recall debugging this same issue before, and I seem to have a local
>version of this commit dated about 6 weeks ago where dma_configure()
>looks like this:
>
>--->8---
>int dma_configure(struct device *dev)
>{
>	struct device *bridge = NULL, *dma_dev = dev;
>
>	if (dev_is_pci(dev)) {
>		bridge = pci_get_host_bridge_device(to_pci_dev(dev));
>		dma_dev = bridge->parent;
>	}
>
>	if (dma_dev && dma_dev->of_node) {
>		of_dma_configure(dev, dma_dev->of_node);
>	} else if (dma_dev && has_acpi_companion(dma_dev)) {
>		struct acpi_device *adev = to_acpi_device_node(dma_dev->fwnode);
>		enum dev_dma_attr attr = acpi_get_dma_attr(adev);
>
>		if (attr == DEV_DMA_NOT_SUPPORTED)
>			dev_warn(dev, "DMA not supported.\n");
>		else
>			arch_setup_dma_ops(dev, 0, 0, NULL,
>					   attr == DEV_DMA_COHERENT);
>	}
>
>	if (bridge)
>		pci_put_host_bridge_device(bridge);
>
>	return 0;
>}
>---8<---
>
>I have a feeling I was having a go at tidying up the "PCI hacks" from v4
>myself, but other things ended up taking precedence.
>

Sure, i will repost with borrowing the names.

Regards,
 Sricharan

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