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backlight: fix issue on multiple graphics cards system
If a system has multiple graphics cards, then we cannot associate platform backlight devices to backlight devices under PCI bus. Previously, in such case, vaidate_device() for a raw backlight device might erroneously detect a platform device and return false. So, users could not save/load backlight level. This makes validate_device() give up to associate platform devices on non-PCI bus with raw backlight devices. That may cause unwanted backlight level save or restore by systemd-backlight@.service, but users can workaround that by masking specific instances of the service. Closes #24223.
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@ -21,6 +21,8 @@
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#include "terminal-util.h"
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#include "util.h"
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#define PCI_CLASS_GRAPHICS_CARD 0x30000
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static int help(void) {
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_cleanup_free_ char *link = NULL;
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int r;
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@ -44,6 +46,47 @@ static int help(void) {
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return 0;
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}
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static int has_multiple_graphics_cards(void) {
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_cleanup_(sd_device_enumerator_unrefp) sd_device_enumerator *e = NULL;
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sd_device *dev;
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bool found = false;
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int r;
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r = sd_device_enumerator_new(&e);
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if (r < 0)
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return r;
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r = sd_device_enumerator_add_match_subsystem(e, "pci", /* match = */ true);
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if (r < 0)
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return r;
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/* class is an unsigned number, let's validate the value later. */
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r = sd_device_enumerator_add_match_sysattr(e, "class", NULL, /* match = */ true);
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if (r < 0)
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return r;
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FOREACH_DEVICE(e, dev) {
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const char *s;
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unsigned long c;
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if (sd_device_get_sysattr_value(dev, "class", &s) < 0)
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continue;
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if (safe_atolu(s, &c) < 0)
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continue;
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if (c != PCI_CLASS_GRAPHICS_CARD)
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continue;
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if (found)
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return true; /* This is the second device. */
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found = true; /* Found the first device. */
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}
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return false;
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}
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static int find_pci_or_platform_parent(sd_device *device, sd_device **ret) {
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const char *subsystem, *sysname, *value;
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sd_device *parent;
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@ -86,7 +129,7 @@ static int find_pci_or_platform_parent(sd_device *device, sd_device **ret) {
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value, subsystem, sysname);
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/* Graphics card */
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if (class == 0x30000) {
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if (class == PCI_CLASS_GRAPHICS_CARD) {
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*ret = parent;
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return 0;
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}
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@ -200,6 +243,23 @@ static int validate_device(sd_device *device) {
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if (r < 0)
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return log_debug_errno(r, "Failed to add sysattr match: %m");
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if (streq(subsystem, "pci")) {
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r = has_multiple_graphics_cards();
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if (r < 0)
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return log_debug_errno(r, "Failed to check if the system has multiple graphics cards: %m");
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if (r > 0) {
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/* If the system has multiple graphics cards, then we cannot associate platform
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* devices on non-PCI bus (especially WMI bus) with PCI devices. Let's ignore all
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* backlight devices that do not have the same parent PCI device. */
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log_debug("Found multiple graphics cards on PCI bus. "
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"Skipping to associate platform backlight devices on non-PCI bus.");
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r = sd_device_enumerator_add_match_parent(enumerate, parent);
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if (r < 0)
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return log_debug_errno(r, "Failed to add parent match: %m");
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}
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}
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FOREACH_DEVICE(enumerate, other) {
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const char *other_subsystem;
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sd_device *other_parent;
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