Re: [PATCH] misc: sram: Only map reserved areas in Tegra SYSRAM

Mikko Perttunen <cyndis@xxxxxxxx> · Thu, 17 Jun 2021 14:40:49 +0300

On 6/17/21 2:00 PM, Greg KH wrote:
On Thu, Jun 17, 2021 at 12:48:04PM +0300, Mikko Perttunen wrote:
On Tegra186 and later, a portion of the SYSRAM may be reserved for use
by TZ. Non-TZ memory accesses to this portion, including speculative
accesses, trigger SErrors that bring down the system. This does also
happen in practice occasionally (due to speculative accesses).

To fix the issue, add a flag to the SRAM driver to only map the
device tree-specified reserved areas depending on a flag set
based on the compatibility string. This would not affect non-Tegra
systems that rely on the entire thing being memory mapped.

Signed-off-by: Mikko Perttunen <mperttunen@xxxxxxxxxx>
---
  drivers/misc/sram.c | 108 +++++++++++++++++++++++++++++++-------------
  drivers/misc/sram.h |   9 ++++
  2 files changed, 86 insertions(+), 31 deletions(-)

diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
index 93638ae2753a..a27ffb3dbea8 100644
--- a/drivers/misc/sram.c
+++ b/drivers/misc/sram.c
@@ -97,7 +97,24 @@ static int sram_add_partition(struct sram_dev *sram, struct sram_reserve *block,
  	struct sram_partition *part = &sram->partition[sram->partitions];
  
  	mutex_init(&part->lock);
-	part->base = sram->virt_base + block->start;
+
+	if (sram->config->map_only_reserved) {
+		void *virt_base;
+
+		if (sram->no_memory_wc)
+			virt_base = devm_ioremap_resource(sram->dev, &block->res);
+		else
+			virt_base = devm_ioremap_resource_wc(sram->dev, &block->res);
+
+		if (IS_ERR(virt_base)) {
+			dev_err(sram->dev, "could not map SRAM at %pr\n", &block->res);
+			return PTR_ERR(virt_base);
+		}
+
+		part->base = virt_base;
+	} else {
+		part->base = sram->virt_base + block->start;
+	}
  
  	if (block->pool) {
  		ret = sram_add_pool(sram, block, start, part);
@@ -198,6 +215,7 @@ static int sram_reserve_regions(struct sram_dev *sram, struct resource *res)
  
  		block->start = child_res.start - res->start;
  		block->size = resource_size(&child_res);
+		block->res = child_res;
  		list_add_tail(&block->list, &reserve_list);
  
  		if (of_find_property(child, "export", NULL))
@@ -295,15 +313,17 @@ static int sram_reserve_regions(struct sram_dev *sram, struct resource *res)
  		 */
  		cur_size = block->start - cur_start;
  
-		dev_dbg(sram->dev, "adding chunk 0x%lx-0x%lx\n",
-			cur_start, cur_start + cur_size);
+		if (sram->pool) {
+			dev_dbg(sram->dev, "adding chunk 0x%lx-0x%lx\n",
+				cur_start, cur_start + cur_size);
  
-		ret = gen_pool_add_virt(sram->pool,
-				(unsigned long)sram->virt_base + cur_start,
-				res->start + cur_start, cur_size, -1);
-		if (ret < 0) {
-			sram_free_partitions(sram);
-			goto err_chunks;
+			ret = gen_pool_add_virt(sram->pool,
+					(unsigned long)sram->virt_base + cur_start,
+					res->start + cur_start, cur_size, -1);
+			if (ret < 0) {
+				sram_free_partitions(sram);
+				goto err_chunks;
+			}
  		}
  
  		/* next allocation after this reserved block */
@@ -331,40 +351,66 @@ static int atmel_securam_wait(void)
  					10000, 500000);
  }
  
+static const struct sram_config default_config = {
+};

No need for a "default" config, just do not provide one and then do not
call it if it is not set.  Much simpler and less code churn.

Sure, will do.



+
+static const struct sram_config atmel_securam_config = {
+	.init = atmel_securam_wait

Add a trailing , please.

Will do.


+};
+
+/*
+ * SYSRAM contains areas that are not accessible by the
+ * kernel, such as the first 256K that is reserved for TZ.
+ * Accesses to those areas (including speculative accesses)
+ * trigger SErrors. As such we must map only the areas of
+ * SYSRAM specified in the device tree.
+ */
+static const struct sram_config tegra_sysram_config = {
+	.map_only_reserved = true,
+};
+
  static const struct of_device_id sram_dt_ids[] = {
-	{ .compatible = "mmio-sram" },
-	{ .compatible = "atmel,sama5d2-securam", .data = atmel_securam_wait },
+	{ .compatible = "mmio-sram", .data = &default_config },
+	{ .compatible = "atmel,sama5d2-securam", .data = &atmel_securam_config },
+	{ .compatible = "nvidia,tegra186-sysram", .data = &tegra_sysram_config },
+	{ .compatible = "nvidia,tegra194-sysram", .data = &tegra_sysram_config },
  	{}
  };
  
  static int sram_probe(struct platform_device *pdev)
  {
+	const struct sram_config *config;
  	struct sram_dev *sram;
  	int ret;
  	struct resource *res;
-	int (*init_func)(void);
+
+	config = of_device_get_match_data(&pdev->dev);
  
  	sram = devm_kzalloc(&pdev->dev, sizeof(*sram), GFP_KERNEL);
  	if (!sram)
  		return -ENOMEM;
  
  	sram->dev = &pdev->dev;
+	sram->no_memory_wc = of_property_read_bool(pdev->dev.of_node, "no-memory-wc");
+	sram->config = config;
+
+	if (!config->map_only_reserved) {
+		res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+		if (sram->no_memory_wc)
+			sram->virt_base = devm_ioremap_resource(&pdev->dev, res);
+		else
+			sram->virt_base = devm_ioremap_resource_wc(&pdev->dev, res);
+		if (IS_ERR(sram->virt_base)) {
+			dev_err(&pdev->dev, "could not map SRAM registers\n");
+			return PTR_ERR(sram->virt_base);
+		}
  
-	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-	if (of_property_read_bool(pdev->dev.of_node, "no-memory-wc"))
-		sram->virt_base = devm_ioremap_resource(&pdev->dev, res);
-	else
-		sram->virt_base = devm_ioremap_resource_wc(&pdev->dev, res);
-	if (IS_ERR(sram->virt_base)) {
-		dev_err(&pdev->dev, "could not map SRAM registers\n");
-		return PTR_ERR(sram->virt_base);
+		sram->pool = devm_gen_pool_create(sram->dev, ilog2(SRAM_GRANULARITY),
+						  NUMA_NO_NODE, NULL);
+		if (IS_ERR(sram->pool))
+			return PTR_ERR(sram->pool);
  	}
  
-	sram->pool = devm_gen_pool_create(sram->dev, ilog2(SRAM_GRANULARITY),
-					  NUMA_NO_NODE, NULL);
-	if (IS_ERR(sram->pool))
-		return PTR_ERR(sram->pool);
-
  	sram->clk = devm_clk_get(sram->dev, NULL);
  	if (IS_ERR(sram->clk))
  		sram->clk = NULL;
@@ -378,15 +424,15 @@ static int sram_probe(struct platform_device *pdev)
  
  	platform_set_drvdata(pdev, sram);
  
-	init_func = of_device_get_match_data(&pdev->dev);
-	if (init_func) {
-		ret = init_func();
+	if (config->init) {
+		ret = config->init();
  		if (ret)
  			goto err_free_partitions;
  	}
  
-	dev_dbg(sram->dev, "SRAM pool: %zu KiB @ 0x%p\n",
-		gen_pool_size(sram->pool) / 1024, sram->virt_base);
+	if (sram->pool)
+		dev_dbg(sram->dev, "SRAM pool: %zu KiB @ 0x%p\n",
+			gen_pool_size(sram->pool) / 1024, sram->virt_base);
  
  	return 0;
  
@@ -405,7 +451,7 @@ static int sram_remove(struct platform_device *pdev)
  
  	sram_free_partitions(sram);
  
-	if (gen_pool_avail(sram->pool) < gen_pool_size(sram->pool))
+	if (sram->pool && gen_pool_avail(sram->pool) < gen_pool_size(sram->pool))
  		dev_err(sram->dev, "removed while SRAM allocated\n");
  
  	if (sram->clk)
diff --git a/drivers/misc/sram.h b/drivers/misc/sram.h
index 9c1d21ff7347..d2058d8c8f1d 100644
--- a/drivers/misc/sram.h
+++ b/drivers/misc/sram.h
@@ -5,6 +5,11 @@
  #ifndef __SRAM_H
  #define __SRAM_H
  
+struct sram_config {
+	int (*init)(void);
+	bool map_only_reserved;
+};
+
  struct sram_partition {
  	void __iomem *base;
  
@@ -15,8 +20,11 @@ struct sram_partition {
  };
  
  struct sram_dev {
+	const struct sram_config *config;
+
  	struct device *dev;
  	void __iomem *virt_base;
+	bool no_memory_wc;

What does "wc" here mean?

Writecombine. The code in _probe checks for the "no-memory-wc" flag in 
device tree and if it's set it uses devm_ioremap_resource instead of 
devm_ioremap_resource_wc. Now that the ioremap call can happen outside 
of _probe we need to save this property.


thanks,

greg k-h


Thank you, will send a v2 with changes.

Mikko






