Re: [XEN v1] xen/Arm: Remove the extra assignment

[Ayan Kumar Halder <ayankuma@xxxxxxx>]

On 03/12/2022 18:05, Julien Grall wrote:
> Hi Ayan,
Hi Julien,

> Title: It suggests that this is modifying arch/arm whereas you are 
> updating the Arm part of the ns16550 driver.
> In addition to that, from a reader PoV, it is more important to 
> emphase on the fact the truncation check is removed rather than the 
> extra assignment.
> So I would suggest the following title:
>
> xen/ns16550: Remove unneeded truncation check in the DT init code
Ack
> On 01/12/2022 17:31, Ayan Kumar Halder wrote:
> > As "io_size" and "uart->io_size" are both u64, so there will be no 
> > truncation.
> > Thus, one can remove the ASSERT() and extra assignment.
> >
> > In an earlier commit (7c1de0038895cbc75ebd0caffc5b0f3f03c5ad51),
> Please use 12-digit hash and provide the commit title.
Ack
> > "ns16550.io_size" was u32 and "io_size" was u64. Thus, the ASSERT() 
> > was needed
> > to check if the values are the same.
> > However, in a later commit (c9f8e0aee507bec25104ca5535fde38efae6c6bc),
> Ditto.
Ack
> > "ns16550.io_size" was changed to u64. Thus, the ASSERT() became 
> > redundant.
> Those two paragraphs explaining your reasoning why the truncation 
> check is removed. So I think they should be moved first. Then you can 
> add the initial paragraph to explain the resolution.
> However... I wonder whether it would not be better to switch 'io_size' 
> to paddr_t because, as you said earlier one, on 32-bit ARMv8-R the 
> address is 32-bit. Therefore:
There are some more drivers where this kind of change (ie using paddr_t 
instead of u64) is required. Thus, I wish to send it in a serie where I 
will introduce CONFIG_ARM_PA_32  (to add support for 32 bit physical 
addresses). Also ...
>  1. it sounds pointless to store the size using 64-bit
>  2. the truncation check still make sense (maybe hardened) in the 
> 32-bit ARMv8-R to catch buggy DT.
Yes, but we need a common check for all the drivers/code as the DT gives 
us 64 bit address (ie u64) and this needs to be translated to paddr_t 
(which can be u64 or u32).
Again, as part of serie to introduce CONFIG_ARM_PA_32, I will provide 
the following function to do address translation :-
--- a/xen/arch/arm/include/asm/platform.h
+++ b/xen/arch/arm/include/asm/platform.h
@@ -42,6 +42,32 @@ struct platform_desc {
     unsigned int dma_bitsize;
 };

+int translate_dt_address_size(u64 *dt_addr, u64 *dt_size, paddr_t *addr,
+                               paddr_t *size)
+{
+#ifdef CONFIG_ARM_PA_32
+    if ( dt_addr && (*dt_addr >> PADDR_SHIFT) )
+    {
+        dprintk(XENLOG_ERR, "Error in DT. Invalid address\n");
+        return -ENXIO;
+    }
+
+    if ( dt_size && (*dt_size >> PADDR_SHIFT) )
+    {
+        dprintk(XENLOG_ERR, "Error in DT. Invalid size\n");
+        return -ENXIO;
+    }
+#endif
+
+    if ( dt_addr && addr )
+        *addr = (paddr_t) (*dt_addr);
+
+    if ( dt_size && size )
+        *size = (paddr_t) (*dt_size);
+
+    return 0;
+}

And the drivers would invoke it as follows. For eg exynos5.c

diff --git a/xen/arch/arm/platforms/exynos5.c 
b/xen/arch/arm/platforms/exynos5.c
index 6560507092..15d1df9104 100644
--- a/xen/arch/arm/platforms/exynos5.c
+++ b/xen/arch/arm/platforms/exynos5.c
@@ -42,8 +42,9 @@ static int exynos5_init_time(void)
     void __iomem *mct;
     int rc;
     struct dt_device_node *node;
-    u64 mct_base_addr;
-    u64 size;
+    paddr_t mct_base_addr;
+    paddr_t size;
+    uint64_t dt_mct_base_addr, dt_size;

     node = dt_find_compatible_node(NULL, NULL, "samsung,exynos4210-mct");
     if ( !node )
@@ -52,14 +53,19 @@ static int exynos5_init_time(void)
         return -ENXIO;
     }

-    rc = dt_device_get_address(node, 0, &mct_base_addr, &size);
+    rc = dt_device_get_address(node, 0, &dt_mct_base_addr, &dt_size);
     if ( rc )
     {
         dprintk(XENLOG_ERR, "Error in \"samsung,exynos4210-mct\"\n");
         return -ENXIO;
     }

-    dprintk(XENLOG_INFO, "mct_base_addr: %016llx size: %016llx\n",
+    rc = translate_dt_address_size(&dt_mct_base_addr, &dt_size, 
&mct_base_addr,
+                                   &size);
+    if ( rc )
+        rteturn rc;
+
+    dprintk(XENLOG_INFO, "mct_base_addr: 0x%"PRIpaddr" size: 
0x%"PRIpaddr"\n",
             mct_base_addr, size);

So if this sounds reasonable, we can still remove the truncation as part 
of the current patch.
If you agree, I can send v2 with an updated commit message.

- Ayan

> Cheers,