Hi Simon,

On 04.04.2016 16:53, Stefan Roese wrote:
Hi Simon,

as you seem to be back from vacation (?), we (Bin and myself) would
like to hear your expert comment on a x86 issue I've discovered
while porting the Designware I2C driver to x86. Please see below:

On 28.03.2016 08:01, Bin Meng wrote:
Hi Stefan,

On Mon, Mar 21, 2016 at 10:04 PM, Stefan Roese <s...@denx.de> wrote:
Hi Bin,

On 21.03.2016 13:43, Bin Meng wrote:
On Mon, Mar 21, 2016 at 8:04 PM, Stefan Roese <s...@denx.de> wrote:
Hi Bin,

On 21.03.2016 10:03, Stefan Roese wrote:

<snip>

      static int designware_i2c_probe_chip(struct udevice *bus, uint chip_addr,
@@ -476,14 +519,45 @@ static int designware_i2c_probe(struct udevice *bus)
      {
             struct dw_i2c *priv = dev_get_priv(bus);

+#ifdef CONFIG_X86
+       /* Save base address from PCI BAR */
+       priv->regs = (struct i2c_regs *)
+               dm_pci_map_bar(bus, PCI_BASE_ADDRESS_0, PCI_REGION_MEM);
+       /* Use BayTrail specific timing values */
+       priv->scl_sda_cfg = &byt_config;
+#else

How about:

         if (device_is_on_pci_bus(dev)) {
         do the PCI I2C stuff here;
         }

I've tried this but it generated compilation errors on socfpga, as the
dm_pci_xxx functions are not available there. So it definitely needs
some #ifdef here. I could go with your suggestion and use
#if CONFIG_DM_PCI as well.

See driver/net/designware.c for example.

             /* Save base address from device-tree */
             priv->regs = (struct i2c_regs *)dev_get_addr(bus);
+#endif

Enabling this code for x86 via if (device_is_on_pci_bus(dev)) results
in this ugly compilation warning:

drivers/i2c/designware_i2c.c: In function ‘designware_i2c_probe’:
drivers/i2c/designware_i2c.c:530:16: warning: cast to pointer from integer of 
different size [-Wint-to-pointer-cast]
      priv->regs = (struct i2c_regs *)dev_get_addr(bus);
                   ^

This is because x86 defines fdt_addr_t / phys_addr_t as 64bit. So
I'm wondering, how dev_get_addr() should get used on x86. Has it
been used anywhere here at all? Should we perhaps go back to
a 32bit phy_addr representation again? So that dev_get_addr()
matches the (void *) size again?


dev_get_addr() is being used on x86 drivers. See
ns16550_serial_ofdata_to_platdata() for example. There is no build
warning for the ns16550 driver.

Looking closer, the warning does not occur here, since the registers
are stored in a u32 variable "base". And assigning a 64bit value to a
32bit variable as in "plat->base = addr" in ns16550.c does not cause any
warnings.

Here in the I2C driver though, the base address is stored as a pointer
(pointer size is 32 bit for x86). And this triggers this warning, even
though its effectively the same assignment. I could cast to u32 but this
would cause problems on 64 bit architectures using this driver (in the
future). So I came up with this approach:

Thanks for digging out these.


/*
   * On x86, "fdt_addr_t" is 64bit but "void *" only 32bit. So assigning the
   * register base directly in dev_get_addr() results in this compilation 
warning:
   *     warning: cast to pointer from integer of different size
   *
   * Using this macro POINTER_SIZE_CAST, allows us to cast the result of
   * dev_get_addr() into a 32bit value before casting it to the pointer
   * (struct i2c_regs *).
   */
#ifdef CONFIG_X86
#define POINTER_SIZE_CAST       u32
#endif

...

static int designware_i2c_probe(struct udevice *bus)
{
          struct dw_i2c *priv = dev_get_priv(bus);

          if (device_is_on_pci_bus(bus)) {
#ifdef CONFIG_DM_PCI
                  /* Save base address from PCI BAR */
                  priv->regs = (struct i2c_regs *)
                          dm_pci_map_bar(bus, PCI_BASE_ADDRESS_0, 
PCI_REGION_MEM);
#ifdef CONFIG_X86
                  /* Use BayTrail specific timing values */
                  priv->scl_sda_cfg = &byt_config;
#endif
#endif
          } else {
                  /* Save base address from device-tree */
                  priv->regs = (struct i2c_regs 
*)(POINTER_SIZE_CAST)dev_get_addr(bus);
          }

But I'm not 100% happy with this approach.


Yes, it's annoying.

So what are the alternatives:

a) Don't compile the  dev_get_addr() part for x86 similar to what I've
     done in v1

b) This approach with POINTER_SIZE_CAST

Any preferences of other ideas?

Side note: My general feeling is, that dev_get_addr() should be able to
get cast into a pointer on all platforms. This is how it is used in many
drivers, btw. Since this is not possible on x86, we might have a problem
here. Simon might have some ideas on this as well...


I would like to hear Simon's input. Simon?

Yes, Simon, what do you think?

Please also see my v2 of this patch which uses (__UINTPTR_TYPE__)
for the cast:

https://patchwork.ozlabs.org/patch/601113/

Simon, could you please take a quick look at this patch? With the
general problem of dev_get_addr() on x86 (as described above). Do you
have some other suggestions to solve this? Or is the solution in
v2 which uses (__UINTPTR_TYPE__) acceptable?

https://patchwork.ozlabs.org/patch/601113/

Thanks,
Stefan

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