drm/i915: add force_probe module parameter to replace alpha_support

The i915.alpha_support module parameter has caused some confusion along
the way. Add new i915.force_probe parameter to specify PCI IDs of
devices to probe, when the devices are recognized but not automatically
probed by the driver. The name is intended to reflect what the parameter
effectively does, avoiding any overloaded semantics of "alpha" and
"support".

The parameter supports "" to disable, "<pci-id>,[<pci-id>,...]" to
enable force probe for one or more devices, and "*" to enable force
probe for all known devices.

Also add new CONFIG_DRM_I915_FORCE_PROBE config option to replace the
DRM_I915_ALPHA_SUPPORT option. This defaults to "*" if
DRM_I915_ALPHA_SUPPORT=y.

Instead of replacing i915.alpha_support immediately, let the two coexist
for a while, with a deprecation message, for a transition period.

Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190506134801.28751-1-jani.nikula@intel.com

drivers/gpu/drm/i915/Kconfig

@@ -45,19 +45,28 @@ config DRM_I915
 config DRM_I915_ALPHA_SUPPORT
 	bool "Enable alpha quality support for new Intel hardware by default"
 	depends on DRM_I915
-	default n
 	help
-	  Choose this option if you have new Intel hardware and want to enable
-	  the alpha quality i915 driver support for the hardware in this kernel
-	  version. You can also enable the support at runtime using the module
-	  parameter i915.alpha_support=1; this option changes the default for
-	  that module parameter.
+	  This option is deprecated. Use DRM_I915_FORCE_PROBE option instead.
 
-	  It is recommended to upgrade to a kernel version with proper support
-	  as soon as it is available. Generally fixes for platforms with alpha
-	  support are not backported to older kernels.
+config DRM_I915_FORCE_PROBE
+	string "Force probe driver for selected new Intel hardware"
+	depends on DRM_I915
+	default "*" if DRM_I915_ALPHA_SUPPORT
+	help
+	  This is the default value for the i915.force_probe module
+	  parameter. Using the module parameter overrides this option.
 
-	  If in doubt, say "N".
+	  Force probe the driver for new Intel graphics devices that are
+	  recognized but not properly supported by this kernel version. It is
+	  recommended to upgrade to a kernel version with proper support as soon
+	  as it is available.
+
+	  Use "" to disable force probe. If in doubt, use this.
+
+	  Use "<pci-id>[,<pci-id>,...]" to force probe the driver for listed
+	  devices. For example, "4500" or "4500,4571".
+
+	  Use "*" to force probe the driver for all known devices.
 
 config DRM_I915_CAPTURE_ERROR
 	bool "Enable capturing GPU state following a hang"

drivers/gpu/drm/i915/i915_drv.h

@@ -2340,8 +2340,6 @@ IS_SUBPLATFORM(const struct drm_i915_private *i915,
 #define IS_ICL_WITH_PORT_F(dev_priv) \
 	IS_SUBPLATFORM(dev_priv, INTEL_ICELAKE, INTEL_SUBPLATFORM_PORTF)
 
-#define IS_ALPHA_SUPPORT(intel_info) ((intel_info)->is_alpha_support)
-
 #define SKL_REVID_A0		0x0
 #define SKL_REVID_B0		0x1
 #define SKL_REVID_C0		0x2

drivers/gpu/drm/i915/i915_params.c

@@ -87,9 +87,12 @@ i915_param_named_unsafe(enable_psr, int, 0600,
 	"(0=disabled, 1=enabled) "
 	"Default: -1 (use per-chip default)");
 
+i915_param_named_unsafe(force_probe, charp, 0400,
+	"Force probe the driver for specified devices. "
+	"See CONFIG_DRM_I915_FORCE_PROBE for details.");
+
 i915_param_named_unsafe(alpha_support, bool, 0400,
-	"Enable alpha quality driver support for latest hardware. "
-	"See also CONFIG_DRM_I915_ALPHA_SUPPORT.");
+	"Deprecated. See i915.force_probe.");
 
 i915_param_named_unsafe(disable_power_well, int, 0400,
 	"Disable display power wells when possible "

drivers/gpu/drm/i915/i915_params.h

@@ -64,6 +64,7 @@ struct drm_printer;
 	param(int, reset, 2) \
 	param(unsigned int, inject_load_failure, 0) \
 	param(int, fastboot, -1) \
+	param(char *, force_probe, CONFIG_DRM_I915_FORCE_PROBE) \
 	/* leave bools at the end to not create holes */ \
 	param(bool, alpha_support, IS_ENABLED(CONFIG_DRM_I915_ALPHA_SUPPORT)) \
 	param(bool, enable_hangcheck, true) \

drivers/gpu/drm/i915/i915_pci.c

@@ -760,7 +760,7 @@ static const struct intel_device_info intel_icelake_11_info = {
 static const struct intel_device_info intel_elkhartlake_info = {
 	GEN11_FEATURES,
 	PLATFORM(INTEL_ELKHARTLAKE),
-	.is_alpha_support = 1,
+	.require_force_probe = 1,
 	.engine_mask = BIT(RCS0) | BIT(BCS0) | BIT(VCS0),
 	.ppgtt_size = 36,
 };
@@ -854,16 +854,57 @@ static void i915_pci_remove(struct pci_dev *pdev)
 	pci_set_drvdata(pdev, NULL);
 }
 
+/* is device_id present in comma separated list of ids */
+static bool force_probe(u16 device_id, const char *devices)
+{
+	char *s, *p, *tok;
+	bool ret;
+
+	/* FIXME: transitional */
+	if (i915_modparams.alpha_support) {
+		DRM_INFO("i915.alpha_support is deprecated, use i915.force_probe=%04x instead\n",
+			 device_id);
+		return true;
+	}
+
+	if (!devices || !*devices)
+		return false;
+
+	/* match everything */
+	if (strcmp(devices, "*") == 0)
+		return true;
+
+	s = kstrdup(devices, GFP_KERNEL);
+	if (!s)
+		return false;
+
+	for (p = s, ret = false; (tok = strsep(&p, ",")) != NULL; ) {
+		u16 val;
+
+		if (kstrtou16(tok, 16, &val) == 0 && val == device_id) {
+			ret = true;
+			break;
+		}
+	}
+
+	kfree(s);
+
+	return ret;
+}
+
 static int i915_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 {
 	struct intel_device_info *intel_info =
 		(struct intel_device_info *) ent->driver_data;
 	int err;
 
-	if (IS_ALPHA_SUPPORT(intel_info) && !i915_modparams.alpha_support) {
-		DRM_INFO("The driver support for your hardware in this kernel version is alpha quality\n"
-			 "See CONFIG_DRM_I915_ALPHA_SUPPORT or i915.alpha_support module parameter\n"
-			 "to enable support in this kernel version, or check for kernel updates.\n");
+	if (intel_info->require_force_probe &&
+	    !force_probe(pdev->device, i915_modparams.force_probe)) {
+		DRM_INFO("Your graphics device %04x is not properly supported by the driver in this\n"
+			 "kernel version. To force driver probe anyway, use i915.force_probe=%04x\n"
+			 "module parameter or CONFIG_DRM_I915_FORCE_PROBE=%04x configuration option,\n"
+			 "or (recommended) check for kernel updates.\n",
+			 pdev->device, pdev->device, pdev->device);
 		return -ENODEV;
 	}
 

drivers/gpu/drm/i915/intel_device_info.h

@@ -105,7 +105,7 @@ enum intel_ppgtt_type {
 #define DEV_INFO_FOR_EACH_FLAG(func) \
 	func(is_mobile); \
 	func(is_lp); \
-	func(is_alpha_support); \
+	func(require_force_probe); \
 	/* Keep has_* in alphabetical order */ \
 	func(has_64bit_reloc); \
 	func(gpu_reset_clobbers_display); \