Hi Simon.
On 20.04.2016 16:40, Simon Glass wrote:
On 11 April 2016 at 09:03, Stefan Roese sr@denx.de wrote:
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 sr@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 sr@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:
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?
I feel that you should store the return value from dev_get_addr() in an fdt_addr_t or a ulong. Then it can be cast to a pointer as you wish. Platform data should hold the ulong, and private data (dev_get_priv()) should hold the pointer.
I'm not keen on the POINTER_SIZE_CAST idea.
Does that fix the problem?
Yes, it does. In a somewhat less ugly way. This is my current result:
} else { ulong base;
/* Save base address from device-tree */
/* * 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 an intermediate "ulong" variable before assigning * this pointer to the "regs" variable solves this issue. */ base = dev_get_addr(bus); priv->regs = (struct i2c_regs *)base; }
If you think this is acceptable, I'll send a new patch version to the list.
Thanks, Stefan