[PATCH v2 4/5] drm/i915/dmc: change how to disable DMC firmware using module param

[Gustavo Sousa]

Quoting Jani Nikula (2024-04-19 06:41:57-03:00)
>The distinction between the dmc_firmware_path module param being NULL
>and the empty string "" is problematic. It's not possible to set the
>parameter back to NULL via sysfs or debugfs. Remove the distinction, and
>consider NULL and the empty string to be the same thing, and use the
>platform default for them.
>
>This removes the possibility to disable DMC (and runtime PM) via
>i915.dmc_firmware_path="". Instead, use "/dev/null" as the magic
>firmware path to skip DMC firmware loading and disable runtime PM.
>
>v2: Add support for i915.dmc_firmware_path="/dev/null" (Gustavo)
>
>Cc: Gustavo Sousa <gustavo.sousa at intel.com>
>Cc: Lucas De Marchi <lucas.demarchi at intel.com>
>Signed-off-by: Jani Nikula <jani.nikula at intel.com>

Reviewed-by: Gustavo Sousa <gustavo.sousa at intel.com>

>---
> drivers/gpu/drm/i915/display/intel_dmc.c | 31 +++++++++++++++++-------
> drivers/gpu/drm/i915/i915_params.c       |  3 ++-
> 2 files changed, 24 insertions(+), 10 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/display/intel_dmc.c b/drivers/gpu/drm/i915/display/intel_dmc.c
>index a2027c6cf4f1..7dabfaa636e4 100644
>--- a/drivers/gpu/drm/i915/display/intel_dmc.c
>+++ b/drivers/gpu/drm/i915/display/intel_dmc.c
>@@ -73,6 +73,21 @@ static struct intel_dmc *i915_to_dmc(struct drm_i915_private *i915)
>         return i915->display.dmc.dmc;
> }
> 
>+static const char *dmc_firmware_param(struct drm_i915_private *i915)
>+{
>+        const char *p = i915->params.dmc_firmware_path;
>+
>+        return p && *p ? p : NULL;
>+}
>+
>+static bool dmc_firmware_param_disabled(struct drm_i915_private *i915)
>+{
>+        const char *p = dmc_firmware_param(i915);
>+
>+        /* Magic path to indicate disabled */
>+        return p && !strcmp(p, "/dev/null");
>+}
>+
> #define DMC_VERSION(major, minor)        ((major) << 16 | (minor))
> #define DMC_VERSION_MAJOR(version)        ((version) >> 16)
> #define DMC_VERSION_MINOR(version)        ((version) & 0xffff)
>@@ -991,7 +1006,7 @@ static void dmc_load_work_fn(struct work_struct *work)
> 
>         err = request_firmware(&fw, dmc->fw_path, i915->drm.dev);
> 
>-        if (err == -ENOENT && !i915->params.dmc_firmware_path) {
>+        if (err == -ENOENT && !dmc_firmware_param(i915)) {
>                 fallback_path = dmc_fallback_path(i915);
>                 if (fallback_path) {
>                         drm_dbg_kms(&i915->drm, "%s not found, falling back to %s\n",
>@@ -1064,16 +1079,14 @@ void intel_dmc_init(struct drm_i915_private *i915)
> 
>         dmc->fw_path = dmc_firmware_default(i915, &dmc->max_fw_size);
> 
>-        if (i915->params.dmc_firmware_path) {
>-                if (strlen(i915->params.dmc_firmware_path) == 0) {
>-                        drm_info(&i915->drm,
>-                                 "Disabling DMC firmware and runtime PM\n");
>-                        goto out;
>-                }
>-
>-                dmc->fw_path = i915->params.dmc_firmware_path;
>+        if (dmc_firmware_param_disabled(i915)) {
>+                drm_info(&i915->drm, "Disabling DMC firmware and runtime PM\n");
>+                goto out;
>         }
> 
>+        if (dmc_firmware_param(i915))
>+                dmc->fw_path = dmc_firmware_param(i915);
>+
>         if (!dmc->fw_path) {
>                 drm_dbg_kms(&i915->drm,
>                             "No known DMC firmware for platform, disabling runtime PM\n");
>diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
>index de43048543e8..edfd1f54a882 100644
>--- a/drivers/gpu/drm/i915/i915_params.c
>+++ b/drivers/gpu/drm/i915/i915_params.c
>@@ -109,7 +109,8 @@ i915_param_named_unsafe(huc_firmware_path, charp, 0400,
>         "HuC firmware path to use instead of the default one");
> 
> i915_param_named_unsafe(dmc_firmware_path, charp, 0400,
>-        "DMC firmware path to use instead of the default one");
>+        "DMC firmware path to use instead of the default one. "
>+        "Use /dev/null to disable DMC and runtime PM.");
> 
> i915_param_named_unsafe(gsc_firmware_path, charp, 0400,
>         "GSC firmware path to use instead of the default one");
>-- 
>2.39.2
>