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Wysocki" Subject: Re: [PATCH v7 4/8] PCI/sysfs: Allow userspace to query and set device reset mechanism Message-ID: <20210619135920.h42gp5ie5c2eutfq@archlinux> References: <20210608054857.18963-5-ameynarkhede03@gmail.com> <20210618200045.GA3141153@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210618200045.GA3141153@bjorn-Precision-5520> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/06/18 03:00PM, Bjorn Helgaas wrote: > On Tue, Jun 08, 2021 at 11:18:53AM +0530, Amey Narkhede wrote: > > Add reset_method sysfs attribute to enable user to > > query and set user preferred device reset methods and > > their ordering. > > Rewrap to fill 75 columns (also apply to other patches if applicable, > e.g., 3/8 looks like it could use it). > > 2/8 looks like it's missing a blank line between paragraphs. > > > Co-developed-by: Alex Williamson > > Signed-off-by: Alex Williamson > > Signed-off-by: Amey Narkhede > > --- > > Documentation/ABI/testing/sysfs-bus-pci | 16 ++++ > > drivers/pci/pci-sysfs.c | 118 ++++++++++++++++++++++++ > > 2 files changed, 134 insertions(+) > > > > diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci > > index ef00fada2..cf6dbbb3c 100644 > > --- a/Documentation/ABI/testing/sysfs-bus-pci > > +++ b/Documentation/ABI/testing/sysfs-bus-pci > > @@ -121,6 +121,22 @@ Description: > > child buses, and re-discover devices removed earlier > > from this part of the device tree. > > > > +What: /sys/bus/pci/devices/.../reset_method > > +Date: March 2021 > > +Contact: Amey Narkhede > > +Description: > > + Some devices allow an individual function to be reset > > + without affecting other functions in the same slot. > > + For devices that have this support, a file named reset_method > > + will be present in sysfs. Reading this file will give names > > + of the device supported reset methods and their ordering. > > + Writing the name or comma separated list of names of any of > > + the device supported reset methods to this file will set the > > + reset methods and their ordering to be used when resetting > > + the device. Writing empty string to this file will disable > > + ability to reset the device and writing "default" will return > > + to the original value. > > Rewrap to fill or add a blank line if "For devices ..." is supposed to > start a new paragraph. > > My guess is you intend reading to show the *currently enabled* reset > methods, not the entire "supported" set? So if a user has disabled > one of them, it no longer appears when you read the file? > > > + > > What: /sys/bus/pci/devices/.../reset > > Date: July 2009 > > Contact: Michael S. Tsirkin > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > > index 316f70c3e..52def79aa 100644 > > --- a/drivers/pci/pci-sysfs.c > > +++ b/drivers/pci/pci-sysfs.c > > @@ -1334,6 +1334,123 @@ static const struct attribute_group pci_dev_rom_attr_group = { > > .is_bin_visible = pci_dev_rom_attr_is_visible, > > }; > > > > +static ssize_t reset_method_show(struct device *dev, > > + struct device_attribute *attr, > > + char *buf) > > +{ > > + struct pci_dev *pdev = to_pci_dev(dev); > > + ssize_t len = 0; > > + int i, prio; > > + > > + for (prio = PCI_RESET_METHODS_NUM; prio; prio--) { > > + for (i = 0; i < PCI_RESET_METHODS_NUM; i++) { > > + if (prio == pdev->reset_methods[i]) { > > + len += sysfs_emit_at(buf, len, "%s%s", > > + len ? "," : "", > > + pci_reset_fn_methods[i].name); > > + break; > > + } > > + } > > + > > + if (i == PCI_RESET_METHODS_NUM) > > + break; > > + } > > I'm guessing that if you adopt the alternate reset_methods[] encoding, > this nested loop becomes a single loop and "prio" goes away? > > > + if (len) > > + len += sysfs_emit_at(buf, len, "\n"); > > + > > + return len; > > +} > > + > > +static ssize_t reset_method_store(struct device *dev, > > + struct device_attribute *attr, > > + const char *buf, size_t count) > > +{ > > + u8 reset_methods[PCI_RESET_METHODS_NUM]; > > + struct pci_dev *pdev = to_pci_dev(dev); > > + u8 prio = PCI_RESET_METHODS_NUM; > > + char *name, *options; > > + int i; > > Reorder decls with to_pci_dev(dev) first, then in order of use. > > > + if (count >= (PAGE_SIZE - 1)) > > + return -EINVAL; > > + > > + options = kstrndup(buf, count, GFP_KERNEL); > > + if (!options) > > + return -ENOMEM; > > + > > + /* > > + * Initialize reset_method such that 0xff indicates > > + * supported but not currently enabled reset methods > > + * as we only use priority values which are within > > + * the range of PCI_RESET_FN_METHODS array size > > + */ > > + for (i = 0; i < PCI_RESET_METHODS_NUM; i++) > > + reset_methods[i] = pdev->reset_methods[i] ? 0xff : 0; > > I'm hoping the 0xff trick goes away with the alternate encoding? > > > + if (sysfs_streq(options, "")) { > > + pci_warn(pdev, "All device reset methods disabled by user"); > > + goto set_reset_methods; > > + } > > I think you can get this case out of the way early with no kstrndup(), > no goto, etc. > > > + if (sysfs_streq(options, "default")) { > > + for (i = 0; i < PCI_RESET_METHODS_NUM; i++) > > + reset_methods[i] = reset_methods[i] ? prio-- : 0; > > + goto set_reset_methods; > > + } > > If you use pci_init_reset_methods() here, you can also get this case > out of the way early. > The problem with alternate encoding is we won't be able to know if one of the reset methods was disabled previously. For example, # cat reset_methods flr,bus # dev->reset_methods = [3, 5, 0, ...] # echo bus > reset_methods # dev->reset_methods = [5, 0, 0, ...] # cat reset_methods bus Now if an user wants to enable flr # echo flr > reset_methods # dev->reset_methods = [3, 0, 0, ...] OR # echo bus,flr > reset_methods # dev->reset_methods = [5, 3, 0, ...] either they need to write "default" first then flr or we will need to reprobe reset methods each time when user writes to reset_method attribute. > > + while ((name = strsep(&options, ",")) != NULL) { > > + if (sysfs_streq(name, "")) > > + continue; > > + > > + name = strim(name); > > + > > + for (i = 0; i < PCI_RESET_METHODS_NUM; i++) { > > + if (reset_methods[i] && > > + sysfs_streq(name, pci_reset_fn_methods[i].name)) { > > + reset_methods[i] = prio--; > > + break; > > + } > > + } > > + > > + if (i == PCI_RESET_METHODS_NUM) { > > + kfree(options); > > + return -EINVAL; > > + } > > + } > > + > > + if (reset_methods[0] && > > + reset_methods[0] != PCI_RESET_METHODS_NUM) > > + pci_warn(pdev, "Device specific reset disabled/de-prioritized by user"); > > Is there a specific reason for this warning? Is it just telling the > user that he might have shot himself in the foot? Not sure that's > necessary. > I think generally presence of device specific reset method means other methods are potentially broken. Is it okay to skip this? > > +set_reset_methods: > > + kfree(options); > > + memcpy(pdev->reset_methods, reset_methods, sizeof(reset_methods)); > > + return count; > > +} > > +static DEVICE_ATTR_RW(reset_method); > > + > > +static struct attribute *pci_dev_reset_method_attrs[] = { > > + &dev_attr_reset_method.attr, > > + NULL, > > +}; > > + > > +static umode_t pci_dev_reset_method_attr_is_visible(struct kobject *kobj, > > + struct attribute *a, int n) > > +{ > > + struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj)); > > + > > + if (!pci_reset_supported(pdev)) > > + return 0; > > I think this _is_visible method is executed only once, at > device_add()-time. That means if a device doesn't support any resets > at that time, "reset_method" will not be visible, and there will be no > way to ever enable a reset method at run-time. I assume that's OK; > just double-checking. > Correct. Its similar to exisitng reset_fn bitfield which is removed in this patch series. [...] Thanks, Amey