linux-kernel - [PATCH v11 5/5] drm/etnaviv: Add support for cached coherent caching mode

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Message-Id: <20231003113356.645394-6-suijingfeng@loongson.cn>
Date:   Tue,  3 Oct 2023 19:33:56 +0800
From:   Sui Jingfeng <suijingfeng@...ngson.cn>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Christian Gmeiner <christian.gmeiner@...il.com>,
        dri-devel@...ts.freedesktop.org, etnaviv@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v11 5/5] drm/etnaviv: Add support for cached coherent caching mode

Loongson CPUs maintain cache coherency by hardware, which means that the
data in the CPU cache is identical to the data in main system memory.
As for the peripheral device, most of Loongson chips choose to define the
peripherals as DMA coherent by default, device drivers do not need to
maintain the coherency between a processor and an I/O device manually.

The above sttement is true for *cached* buffers only, this patch say
nothing about WC buffers, it is likely implement-dependent. WC buffers
can be DMA non-coherent on specific platform.

Also because vivante GPU IP has been integrated into various platform, we
need to do the probe work. this patch add code to test if a specific
platform is cached coherent, utilize such hardware feature where suitable.
And allow userspace to query.

Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
---
 drivers/gpu/drm/etnaviv/etnaviv_drv.c |  7 +++++++
 drivers/gpu/drm/etnaviv/etnaviv_drv.h |  8 ++++++++
 drivers/gpu/drm/etnaviv/etnaviv_gem.c | 16 ++++++++++++++--
 drivers/gpu/drm/etnaviv/etnaviv_gpu.c |  4 ++++
 include/uapi/drm/etnaviv_drm.h        |  1 +
 5 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_drv.c b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
index 8db86120b11d..3598e2f840b3 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_drv.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
@@ -5,6 +5,7 @@
 
 #include <linux/component.h>
 #include <linux/dma-mapping.h>
+#include <linux/dma-map-ops.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
@@ -66,6 +67,12 @@ static struct etnaviv_drm_private *etnaviv_alloc_private(struct device *dev)
 		return ERR_PTR(-ENOMEM);
 	}
 
+	/*
+	 * The device_get_dma_attr(dev) == DEV_DMA_COHERENT don't work
+	 * on LoongArch platform, so still use dev_is_dma_coherent(dev).
+	 */
+	priv->cached_coherent = dev_is_dma_coherent(dev);
+
 	return priv;
 }
 
diff --git a/drivers/gpu/drm/etnaviv/etnaviv_drv.h b/drivers/gpu/drm/etnaviv/etnaviv_drv.h
index 9cd72948cfad..760048c35481 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_drv.h
+++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.h
@@ -46,6 +46,14 @@ struct etnaviv_drm_private {
 	struct xarray active_contexts;
 	u32 next_context_id;
 
+	/*
+	 * If true, the GPU is capable of snooping CPU's cache. It means
+	 * that cached buffer is coherent for both of the CPU and GPU's
+	 * access. And the coherency is guaranteed by platform hardware.
+	 * Software enforced coherency does not count here.
+	 */
+	bool cached_coherent;
+
 	/* list of GEM objects: */
 	struct mutex gem_lock;
 	struct list_head gem_list;
diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
index 71a6d2b1c80f..a72ca0a6883e 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
@@ -342,6 +342,7 @@ void *etnaviv_gem_vmap(struct drm_gem_object *obj)
 static void *etnaviv_gem_vmap_impl(struct etnaviv_gem_object *obj)
 {
 	struct page **pages;
+	pgprot_t prot;
 
 	lockdep_assert_held(&obj->lock);
 
@@ -349,8 +350,19 @@ static void *etnaviv_gem_vmap_impl(struct etnaviv_gem_object *obj)
 	if (IS_ERR(pages))
 		return NULL;
 
-	return vmap(pages, obj->base.size >> PAGE_SHIFT,
-			VM_MAP, pgprot_writecombine(PAGE_KERNEL));
+	switch (obj->flags) {
+	case ETNA_BO_CACHED:
+		prot = PAGE_KERNEL;
+		break;
+	case ETNA_BO_UNCACHED:
+		prot = pgprot_noncached(PAGE_KERNEL);
+		break;
+	case ETNA_BO_WC:
+	default:
+		prot = pgprot_writecombine(PAGE_KERNEL);
+	}
+
+	return vmap(pages, obj->base.size >> PAGE_SHIFT, VM_MAP, prot);
 }
 
 static inline enum dma_data_direction etnaviv_op_to_dma_dir(u32 op)
diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
index 330f8a272184..9530dddd4273 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
@@ -164,6 +164,10 @@ int etnaviv_gpu_get_param(struct etnaviv_gpu *gpu, u32 param, u64 *value)
 		*value = gpu->identity.eco_id;
 		break;
 
+	case ETNAVIV_PARAM_CACHED_COHERENT:
+		*value = priv->cached_coherent;
+		break;
+
 	default:
 		DBG("%s: invalid param: %u", dev_name(gpu->dev), param);
 		return -EINVAL;
diff --git a/include/uapi/drm/etnaviv_drm.h b/include/uapi/drm/etnaviv_drm.h
index af024d90453d..61eaa8cd0f5e 100644
--- a/include/uapi/drm/etnaviv_drm.h
+++ b/include/uapi/drm/etnaviv_drm.h
@@ -77,6 +77,7 @@ struct drm_etnaviv_timespec {
 #define ETNAVIV_PARAM_GPU_PRODUCT_ID                0x1c
 #define ETNAVIV_PARAM_GPU_CUSTOMER_ID               0x1d
 #define ETNAVIV_PARAM_GPU_ECO_ID                    0x1e
+#define ETNAVIV_PARAM_CACHED_COHERENT               0x1f
 
 #define ETNA_MAX_PIPES 4
 
-- 
2.34.1