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Message-ID: <20230816103941.GW22185@unreal> Date: Wed, 16 Aug 2023 13:39:41 +0300 From: Leon Romanovsky <leon@...nel.org> To: Yu Liao <liaoyu15@...wei.com> Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, liwei391@...wei.com, Xiongfeng Wang <wangxiongfeng2@...wei.com> Subject: Re: [PATCH net-next] pds_core: remove redundant pci_clear_master() On Wed, Aug 16, 2023 at 05:39:33PM +0800, Yu Liao wrote: > On 2023/8/16 14:38, Leon Romanovsky wrote: > > On Wed, Aug 16, 2023 at 09:38:02AM +0800, Yu Liao wrote: > >> pci_disable_device() involves disabling PCI bus-mastering. So remove > >> redundant pci_clear_master(). > > > > I would say that this commit message needs to be more descriptive and > > explain why pci_disable_device() will actually disable PCI in these > > flows. > > > > According to the doc and code: > > 2263 * Note we don't actually disable the device until all callers of > > 2264 * pci_enable_device() have called pci_disable_device(). > > > > Thanks > > > Thank you for the review. My bad, I didn't describe it clearly in commit > message. I will send the v2 version and add the following explanation: > > do_pci_disable_device() disable PCI bus-mastering as following: > static void do_pci_disable_device(struct pci_dev *dev) > { > u16 pci_command; > > pci_read_config_word(dev, PCI_COMMAND, &pci_command); > if (pci_command & PCI_COMMAND_MASTER) { > pci_command &= ~PCI_COMMAND_MASTER; > pci_write_config_word(dev, PCI_COMMAND, pci_command); > } > > pcibios_disable_device(dev); > } > And pci_disable_device() sets dev->is_busmaster to 0. > > So for pci_dev that has called pci_enable_device(), pci_disable_device() > involves disabling PCI bus-mastering. Remove redundant pci_clear_master() in > the following places: > - In error path 'err_out_clear_master' of pdsc_probe(), pci_enable_device() > has already been called. > - In pdsc_remove(), pci_enable_device() has already been called in pdsc_probe(). All that you need to add is a sentence that pci_enable_device() is called only once before calling to pci_disable_device() and such pci_clear_master() is not needed. Thanks
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