[PATCH v3 1/2] iommu/shmobile: Add iommu driver for Renesas IPMMU modules

Hi,

From: Nobuhiro Iwamatsu <redacted>
Subject: Re: [PATCH v3 1/2] iommu/shmobile: Add iommu driver for Renesas IPMMU modules
Date: Wed, 12 Sep 2012 17:07:00 +0900

quoted

+static inline void ipmmu_add_device(struct device *dev)
+{
+}

Please use 'do { } while (0)'.

Do you mean using #define macro is better than this inline function?
I chose the inline function because:

- The function's argument type is checked by a compiler.
- Its output code should be exactly the same as a macro in this case.
- The Linux kernel coding style says "Generally, inline functions are
  preferable to macros resembling functions."

quoted

+       switch (size) {
+       default:
+               priv->tlb_enabled = 0;
+               break;
+       case 0x2000:
+               ipmmu_reg_write(priv, IMTTBCR, 1);
+               priv->tlb_enabled = 1;
+               break;
+       case 0x1000:
+               ipmmu_reg_write(priv, IMTTBCR, 2);
+               priv->tlb_enabled = 1;
+               break;
+       case 0x800:
+               ipmmu_reg_write(priv, IMTTBCR, 3);
+               priv->tlb_enabled = 1;
+               break;
+       case 0x400:
+               ipmmu_reg_write(priv, IMTTBCR, 4);
+               priv->tlb_enabled = 1;
+               break;
+       case 0x200:
+               ipmmu_reg_write(priv, IMTTBCR, 5);
+               priv->tlb_enabled = 1;
+               break;
+       case 0x100:
+               ipmmu_reg_write(priv, IMTTBCR, 6);
+               priv->tlb_enabled = 1;
+               break;
+       case 0x80:
+               ipmmu_reg_write(priv, IMTTBCR, 7);
+               priv->tlb_enabled = 1;
+               break;
+       }

I thought that you could describe more briefly if ffs() is used.

This is simply converted from a hardware manual.  ffs() can be used
like below:

	bit = ffs(size);
	if (bit >= 7 && bit <= 13 && (1 << bit) == size) {
		ipmmu_reg_write(priv, IMTTBCR, 14 - bit);
		priv->tlb_enabled = 1;
	} else {
		priv->tlb_enabled = 0;
	}

Checking size is still needed because only 7 sizes are allowed here.
I think using switch() is easier to understand.

quoted

+#ifdef CONFIG_SHMOBILE_IOMMU_L1SIZE_8192
+#define L1_SIZE 8192
+#endif
+#ifdef CONFIG_SHMOBILE_IOMMU_L1SIZE_4096
+#define L1_SIZE 4096
+#endif
+#ifdef CONFIG_SHMOBILE_IOMMU_L1SIZE_2048
+#define L1_SIZE 2048
+#endif
+#ifdef CONFIG_SHMOBILE_IOMMU_L1SIZE_1024
+#define L1_SIZE 1024
+#endif
+#ifdef CONFIG_SHMOBILE_IOMMU_L1SIZE_512
+#define L1_SIZE 512
+#endif
+#ifdef CONFIG_SHMOBILE_IOMMU_L1SIZE_256
+#define L1_SIZE 256
+#endif
+#ifdef CONFIG_SHMOBILE_IOMMU_L1SIZE_128
+#define L1_SIZE 128
+#endif

I think that it was better to define by kconfig.
For example, following codes.

+config SHMOBILE_IOMMU_L1SIZE
+       hex
+       default "0x00002000" if SHMOBILE_IOMMU_L1SIZE_8192
+       default "0x00001000" if SHMOBILE_IOMMU_L1SIZE_4096
+       default "0x00000800" if SHMOBILE_IOMMU_L1SIZE_2048
+       default "0x00000400" if SHMOBILE_IOMMU_L1SIZE_1024
+       default "0x00000200" if SHMOBILE_IOMMU_L1SIZE_512
+       default "0x00000100" if SHMOBILE_IOMMU_L1SIZE_256
+       default "0x00000080" if SHMOBILE_IOMMU_L1SIZE_128

I did not know that way.  It looks good for me too.
Thank you.

-- 
Hideki EIRAKU [off-list ref]