linux-kernel - Re: [PATCH v2 1/2] drm: allow limiting the scatter list size.

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Date:   Mon, 7 Sep 2020 08:39:01 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     dri-devel@...ts.freedesktop.org, christian.koenig@....com,
        Alex Deucher <alexander.deucher@....com>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Lucas Stach <l.stach@...gutronix.de>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Ben Skeggs <bskeggs@...hat.com>,
        Sandy Huang <hjc@...k-chips.com>,
        Heiko Stübner <heiko@...ech.de>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        "open list:RADEON and AMDGPU DRM DRIVERS" 
        <amd-gfx@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:DRM DRIVERS FOR VIVANTE GPU IP" 
        <etnaviv@...ts.freedesktop.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <freedreno@...ts.freedesktop.org>,
        "open list:DRM DRIVER FOR NVIDIA GEFORCE/QUADRO GPUS" 
        <nouveau@...ts.freedesktop.org>,
        "moderated list:ARM/Rockchip SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC support" 
        <linux-rockchip@...ts.infradead.org>,
        "open list:DRM DRIVERS FOR NVIDIA TEGRA" 
        <linux-tegra@...r.kernel.org>,
        "moderated list:DRM DRIVERS FOR XEN" <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH v2 1/2] drm: allow limiting the scatter list size.

> > +	/**
> > +	 * @max_segment:
> > +	 *
> > +	 * Max size for scatter list segments.  When unset the default
> > +	 * (SCATTERLIST_MAX_SEGMENT) is used.
> > +	 */
> > +	size_t max_segment;
> 
> Is there no better place for this then "at the bottom"? drm_device is a
> huge structure, piling stuff up randomly doesn't make it better :-)

Moved next to the other gem fields for now (v3 posted).

> I think ideally we'd have a gem substruct like we have on the modeset side
> at least.

Phew, that'll be quite some churn in the tree.  And there aren't that many
gem-related fields in struct drm_device.

So you are looking for something like below (header changes only)?

take care,
  Gerd

diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
index c455ef404ca6..950167ede98a 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -299,22 +299,8 @@ struct drm_device {
 	/** @mode_config: Current mode config */
 	struct drm_mode_config mode_config;
 
-	/** @object_name_lock: GEM information */
-	struct mutex object_name_lock;
-
-	/** @object_name_idr: GEM information */
-	struct idr object_name_idr;
-
-	/** @vma_offset_manager: GEM information */
-	struct drm_vma_offset_manager *vma_offset_manager;
-
-	/**
-	 * @max_segment:
-	 *
-	 * Max size for scatter list segments for GEM objects.  When
-	 * unset the default (SCATTERLIST_MAX_SEGMENT) is used.
-	 */
-	size_t max_segment;
+	/** @gem_config: Current GEM config */
+	struct drm_gem_config gem_config;
 
 	/** @vram_mm: VRAM MM memory manager */
 	struct drm_vram_mm *vram_mm;
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 337a48321705..74129fb29fb8 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -39,6 +39,25 @@
 
 #include <drm/drm_vma_manager.h>
 
+struct drm_gem_config {
+	/** @object_name_lock: GEM information */
+	struct mutex object_name_lock;
+
+	/** @object_name_idr: GEM information */
+	struct idr object_name_idr;
+
+	/** @vma_offset_manager: GEM information */
+	struct drm_vma_offset_manager *vma_offset_manager;
+
+	/**
+	 * @max_segment:
+	 *
+	 * Max size for scatter list segments for GEM objects.  When
+	 * unset the default (SCATTERLIST_MAX_SEGMENT) is used.
+	 */
+	size_t max_segment;
+};
+
 struct drm_gem_object;
 
 /**