Hi Andy, Thanks for your reply ! On 2022/11/23 3:03, Andy Shevchenko wrote: > On Tue, Nov 22, 2022 at 07:45:59PM +0800, Xiongfeng Wang wrote: >> As comment of pci_get_slot() says, it returns a pci_device with its >> refcount increased. The caller must decrement the reference count by >> calling pci_dev_put(). > >> Since 'dma_dev' is only used to filter the channel in filter(), we can >> call pci_dev_put() before exiting from pch_request_dma(). Add the >> missing pci_dev_put() for the normal and error path. > > No, we can't do that. How is it supposed to work if DMA device disappears in > the middle? When the DMA device is registered into the system, its refcount is increased. dma_request_channel() will increase the refcount for 'dma_chan'. So I think this can gurantee the DMA device not removed in the middle. Thanks, Xiongfeng > > Look at how it's done in the > > 5318f70da7e8 serial: 8250_lpss: Balance reference count for PCI DMA device > 67ec6dd0b257 serial: 8250_mid: Balance reference count for PCI DMA device >
