[Intel-gfx] [PATCH 5/8] drm/i915/dmc: don't register DMC debugfs file if there's no DMC

[Lucas De Marchi]

On Thu, Mar 17, 2022 at 08:36:17PM +0200, Jani Nikula wrote:
>Register the DMC debugfs file only on platforms that support
>DMC. There's no point in having a no-op debugfs file.

It seems this would not change much the behavior (fail on open vs fail
on read). But the code in igt is suspicious:


	bool igt_pm_dmc_loaded(int debugfs)
	{
		char buf[15];
		int len;

		len = igt_sysfs_read(debugfs, "i915_dmc_info", buf, sizeof(buf) - 1);
		if (len < 0)
			return true; /* no CSR support, no DMC requirement */

 From a quick inspection of igt_sysfs_read() it seems it would just
return 0 if there's nothing to be read. And it would return < 0 on
failure to open the file.

These would be the affected tests:

tests/i915/i915_pm_rpm.c:
tests/i915/i915_pm_lpsp.c:
tests/i915/i915_pm_dc.c:
	igt_require(igt_pm_dmc_loaded(data.debugfs_fd));


Lucas De Marchi

>
>Signed-off-by: Jani Nikula <jani.nikula at intel.com>
>---
> drivers/gpu/drm/i915/display/intel_dmc.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/display/intel_dmc.c b/drivers/gpu/drm/i915/display/intel_dmc.c
>index 5de13f978e57..8dfa2aa9f8bd 100644
>--- a/drivers/gpu/drm/i915/display/intel_dmc.c
>+++ b/drivers/gpu/drm/i915/display/intel_dmc.c
>@@ -818,9 +818,6 @@ static int intel_dmc_debugfs_status_show(struct seq_file *m, void *unused)
> 	struct intel_dmc *dmc;
> 	i915_reg_t dc5_reg, dc6_reg = INVALID_MMIO_REG;
>
>-	if (!HAS_DMC(i915))
>-		return -ENODEV;
>-
> 	dmc = &i915->dmc;
>
> 	wakeref = intel_runtime_pm_get(&i915->runtime_pm);
>@@ -890,6 +887,9 @@ void intel_dmc_debugfs_register(struct drm_i915_private *i915)
> {
> 	struct drm_minor *minor = i915->drm.primary;
>
>+	if (!HAS_DMC(i915))
>+		return;
>+
> 	debugfs_create_file("i915_dmc_info", 0444, minor->debugfs_root,
> 			    i915, &intel_dmc_debugfs_status_fops);
> }
>-- 
>2.30.2
>