Re: [PATCH 10/10] ufs: fix DMA mask setting

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On 6/29/2013 11:10 AM, Akinobu Mita wrote:
2013/6/29 James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>:
On Wed, 2013-06-26 at 22:39 +0530, Santosh Y wrote:
index 19618c6..431ddb2 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -1711,6 +1711,25 @@ void ufshcd_remove(struct ufs_hba *hba)
  EXPORT_SYMBOL_GPL(ufshcd_remove);

  /**
+ * ufshcd_set_dma_mask - Set dma mask based on the controller
+ *                    addressing capability
+ * @hba: per adapter instance
+ *
+ * Returns 0 for success, non-zero for failure
+ */
+static int ufshcd_set_dma_mask(struct ufs_hba *hba)
+{
+     if (hba->capabilities & MASK_64_ADDRESSING_SUPPORT) {
+             if (!dma_set_mask(hba->dev, DMA_BIT_MASK(64)) &&
+                 !dma_set_coherent_mask(hba->dev, DMA_BIT_MASK(64)))
+                     return 0;
+     }
+     dma_set_mask(hba->dev, DMA_BIT_MASK(32));
+
+     return dma_set_coherent_mask(hba->dev, DMA_BIT_MASK(32));
+}

This isn't right per the API spec.  The guarantee is that if
dma_set_mask() succeeds then dma_set_coherent_mask of the same mask will
succeed,  so this should read

         int err;

         if (hba->capabilities & MASK_64_ADDRESSING_SUPPORT) {
                 if (!dma_set_mask(hba->dev, DMA_BIT_MASK(64))) {
                         dma_set_coherent_mask(hba->dev, DMA_BIT_MASK(64)))
                         return 0;
                 }
         }
         err = dma_set_mask(hba->dev, DMA_BIT_MASK(32));
         if (!err)
                 dma_set_coherent_mask(hba->dev, DMA_BIT_MASK(32));
         return err;

Thanks for the explanation.  I agree that this is the correct definision
of ufshcd_set_dma_mask().

The reason that I omitted the error check on dma_set_mask(DMA_BIT_MASK(32))
in the patch was that I was seeing that error due to the luck of
valid dev->dma_mask pointer on OF platform devices although
dma_supported(DMA_BIT_MASK(32)) returns true.

The popular trick implemented for device-tree probed devices is -
dev->dma_mask = &dev->coherent_dma_mask;

If you don't agree with this you can have something like -
dev->dma_mask = devm_kzalloc(dev, sizeof(*dev->dma_mask), GFP_KERNEL);
See platform_device_register_full();


However, now I think that I should investigate more about dev->dma_mask
issue rather than jumping into short-circuit fixing in the driver.  And
then I will revisit this.


--
Regards,
Sujit
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