[PATCH 4/5] drm/i915/dmc: change meaning of dmc_firmware_path="" module param

[Lucas De Marchi]

On Thu, Apr 18, 2024 at 05:44:13PM GMT, Gustavo Sousa wrote:
>Quoting Jani Nikula (2024-04-18 17:09:04-03:00)
>>On Thu, 18 Apr 2024, Gustavo Sousa <gustavo.sousa at intel.com> wrote:
>>> Quoting Jani Nikula (2024-04-18 11:39:53-03:00)
>>>>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, you will need to specify a
>>>>non-existent file or a file that will not parse correctly.
>>>>
>>>>Signed-off-by: Jani Nikula <jani.nikula at intel.com>
>>>>---
>>>> drivers/gpu/drm/i915/display/intel_dmc.c | 20 ++++++++++----------
>>>> drivers/gpu/drm/i915/i915_params.c       |  3 ++-
>>>> 2 files changed, 12 insertions(+), 11 deletions(-)
>>>>
>>>>diff --git a/drivers/gpu/drm/i915/display/intel_dmc.c b/drivers/gpu/drm/i915/display/intel_dmc.c
>>>>index 740c05ce83cc..3e510c2be1eb 100644
>>>>--- a/drivers/gpu/drm/i915/display/intel_dmc.c
>>>>+++ b/drivers/gpu/drm/i915/display/intel_dmc.c
>>>>@@ -73,6 +73,13 @@ 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;
>>>>+}
>>>>+
>>>> #define DMC_VERSION(major, minor)        ((major) << 16 | (minor))
>>>> #define DMC_VERSION_MAJOR(version)        ((version) >> 16)
>>>> #define DMC_VERSION_MINOR(version)        ((version) & 0xffff)
>>>>@@ -989,7 +996,7 @@ 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",
>>>>@@ -1062,15 +1069,8 @@ 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(i915))
>>>>+                dmc->fw_path = dmc_firmware_param(i915);
>>>>
>>>>         if (!dmc->fw_path) {
>>>>                 drm_dbg_kms(&i915->drm,
>>>>diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
>>>>index de43048543e8..9e7f2a9f6287 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 non-existent file to disable DMC and runtime PM.");
>>>
>>> Okay. But is it too bad to have a magic string for it? The up side is
>>> that there wouldn't be error messages in the log if we had such option.
>>
>>Another upside is that we could also just skip requesting the firmware
>>altogether, similar to what we have currently.
>>
>>It's just a small naming problem... what should the magic string for
>>"disabled" be? Like, yes, that's the obvious choice right there, but
>>it's also a valid filename. Who am I to say how people should name their
>>firmware blobs. :)
>>
>>"/dev/null"?
>
>I like this one!

+1

Lucas De Marchi