drm/v3d: Add clock handling

Since the initial commit 57692c94dcbe ("drm/v3d: Introduce a new DRM driver
for Broadcom V3D V3.x+") the struct v3d_dev reserved a pointer for
an optional V3D clock. But there wasn't any code, which fetched it.
So add the missing clock handling before accessing any V3D registers.

Signed-off-by: Stefan Wahren <[e-mail]>
Reviewed-by: Maíra Canal <[e-mail]>
Signed-off-by: Maíra Canal <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/v3d/v3d_drv.c

···
 	if (ret)
 		return ret;
 
+	v3d->clk = devm_clk_get_optional(dev, NULL);
+	if (IS_ERR(v3d->clk))
+		return dev_err_probe(dev, PTR_ERR(v3d->clk), "Failed to get V3D clock\n");
+
+	ret = clk_prepare_enable(v3d->clk);
+	if (ret) {
+		dev_err(&pdev->dev, "Couldn't enable the V3D clock\n");
+		return ret;
+	}
+
 	mmu_debug = V3D_READ(V3D_MMU_DEBUG_INFO);
 	mask = DMA_BIT_MASK(30 + V3D_GET_FIELD(mmu_debug, V3D_MMU_PA_WIDTH));
 	ret = dma_set_mask_and_coherent(dev, mask);
 	if (ret)
-		return ret;
+		goto clk_disable;
 
 	v3d->va_width = 30 + V3D_GET_FIELD(mmu_debug, V3D_MMU_VA_WIDTH);
 
···
 		ret = PTR_ERR(v3d->reset);
 
 		if (ret == -EPROBE_DEFER)
-			return ret;
+			goto clk_disable;
 
 		v3d->reset = NULL;
 		ret = map_regs(v3d, &v3d->bridge_regs, "bridge");
 		if (ret) {
 			dev_err(dev,
 				"Failed to get reset control or bridge regs\n");
-			return ret;
+			goto clk_disable;
 		}
 	}
 
 	if (v3d->ver < 41) {
 		ret = map_regs(v3d, &v3d->gca_regs, "gca");
 		if (ret)
-			return ret;
+			goto clk_disable;
 	}
 
 	v3d->mmu_scratch = dma_alloc_wc(dev, 4096, &v3d->mmu_scratch_paddr,
 					GFP_KERNEL | __GFP_NOWARN | __GFP_ZERO);
 	if (!v3d->mmu_scratch) {
 		dev_err(dev, "Failed to allocate MMU scratch page\n");
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto clk_disable;
 	}
 
 	ret = v3d_gem_init(drm);
···
 	v3d_gem_destroy(drm);
 dma_free:
 	dma_free_wc(dev, 4096, v3d->mmu_scratch, v3d->mmu_scratch_paddr);
+clk_disable:
+	clk_disable_unprepare(v3d->clk);
 	return ret;
 }
 
···
 
 	dma_free_wc(v3d->drm.dev, 4096, v3d->mmu_scratch,
 		    v3d->mmu_scratch_paddr);
+
+	clk_disable_unprepare(v3d->clk);
 }
 
 static struct platform_driver v3d_platform_driver = {