Re: [PATCH 1/3] mtd: spi-nor: add optional DMA-safe bounce buffer for data transfer

On Tue, 26 Dec 2017 14:59:00 +0100
Cyrille Pitchen [off-list ref] wrote:

Hi Vignesh

Le 26/12/2017 à 14:42, Vignesh R a écrit :

quoted

Hi Cyrille,

Thanks for doing this series! One comment below.

On 24-Dec-17 10:06 AM, Cyrille Pitchen wrote:
[...]  

quoted

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index 8bafd462f0ae..59f9fbd45234 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c

@@ -14,8 +14,10 @@
 #include <linux/errno.h>
 #include <linux/module.h>
 #include <linux/device.h>
+#include <linux/highmem.h>
 #include <linux/mutex.h>
 #include <linux/math64.h>
+#include <linux/mm.h>
 #include <linux/sizes.h>
 #include <linux/slab.h>
 

@@ -1232,6 +1234,56 @@ static const struct flash_info spi_nor_ids[] = {
 	{ },
 };
 
+static bool spi_nor_is_dma_safe(const void *buf)
+{
+	if (is_vmalloc_addr(buf))
+		return false;
+
+#ifdef CONFIG_HIGHMEM
+	if ((unsigned long)buf >= PKMAP_BASE &&
+	    (unsigned long)buf < (PKMAP_BASE + (LAST_PKMAP * PAGE_SIZE)))
+		return false;
+#endif
+
+	return true;
+}
+  

Better way would be to use virt_addr_valid():
static bool spi_nor_is_dma_safe(const void *buf)
{
	return virt_addr_valid(buf);
}

Regards
Vignesh
  

Thanks for the advice :)

https://patchwork.kernel.org/patch/9768341/
Maybe I could check both virt_addr_valid() and object_is_on_stack() too ?

Yep, see the explanation given here [1].

[1]http://elixir.free-electrons.com/linux/v4.15-rc6/source/Documentation/DMA-API-HOWTO.txt#L132
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