Re: [PATCH] of: calculate masks of the device based on dma-range size

[Murali Karicheri]

On 02/09/2015 06:27 AM, Catalin Marinas wrote:
On Fri, Feb 06, 2015 at 03:15:20PM -0500, Murali Karicheri wrote:
diff --git a/drivers/of/device.c b/drivers/of/device.c
index 314c8a9..44209fa 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -83,17 +83,18 @@ int of_device_add(struct platform_device *ofdev)
   */
  void of_dma_configure(struct device *dev, struct device_node *np)
  {
-       u64 dma_addr, paddr, size;
+       u64 dma_addr = 0, paddr, size;
        int ret;
        bool coherent;
-       unsigned long offset;
+       unsigned long offset = 0;
        struct iommu_ops *iommu;
        /*
         * Set default dma-mask to 32 bit. Drivers are expected to setup
         * the correct supported dma_mask.
         */
-       dev->coherent_dma_mask = DMA_BIT_MASK(32);
+       if (!dev->coherent_dma_mask)
+               dev->coherent_dma_mask = DMA_BIT_MASK(32);

        /*
         * Set it to coherent_dma_mask by default if the architecture
@@ -102,11 +103,14 @@ void of_dma_configure(struct device *dev, struct 
device_node *np)
        if (!dev->dma_mask)
                dev->dma_mask =&dev->coherent_dma_mask;

+       /*
+        * Set default size to cover the 32-bit. Drivers are expected to setup
+        * the correct size and dma_mask.
+        */

Nitpick: drivers don't set up the size, just the mask. We read the size
from DT.

Not sure how this came, I will update this.

+       size = 1ULL<<  32;
+
        ret = of_dma_get_range(np,&dma_addr,&paddr,&size);
-       if (ret<  0) {
-               dma_addr = offset = 0;
-               size = dev->coherent_dma_mask + 1;

Do you assume that, on error, of_dma_get_range() does not touch any of
the dma_addr/paddr/size? It looks safer to me to leave it as the
original.
I think dma_addr and paddr is both modified on error. So this change 
can't be done. I will revert the logic back to original.

-       } else {
+       if (!ret) {
                offset = PFN_DOWN(paddr - dma_addr);

                /*
@@ -128,6 +132,15 @@ void of_dma_configure(struct device *dev, struct 
device_node *np)

        dev->dma_pfn_offset = offset;

+       /*
+        * Limit coherent and dma mask based on size and default mask
+        * set by the driver.
+        */
+       dev->coherent_dma_mask = min(dev->coherent_dma_mask,
+                                    DMA_BIT_MASK(ilog2(dma_addr + size)));

Do we need to cover the case where size is incorrectly set to 0 in the
DT? At least some warning and leaving the mask unchanged.

The previous series already warn and return if the size is incorrect 
(Patch v6 3/7) and leave the dma mask unchanged. So we don't have to do 
anything in this patch. I will fix the above and re-send.

+       *dev->dma_mask = min((*dev->dma_mask),
+                            DMA_BIT_MASK(ilog2(dma_addr + size)));
+
        coherent = of_dma_is_coherent(np);
        dev_dbg(dev, "device is%sdma coherent\n",
                coherent ? " " : " not ");



--
Murali Karicheri
Linux Kernel, Texas Instruments
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