[U-Boot] [PATCH 6/6] i2c: designware_i2c: Add support for PCI(e) based I2C cores (x86)
Stefan Roese
sr at denx.de
Wed Apr 20 17:17:37 CEST 2016
Hi Simon,
On 20.04.2016 17:09, Simon Glass wrote:
> Hi Stefan,
>
> On 20 April 2016 at 08:58, Stefan Roese <sr at denx.de> wrote:
>>
>> Hi Simon.
>>
>> On 20.04.2016 16:40, Simon Glass wrote:
>>
>>> On 11 April 2016 at 09:03, Stefan Roese <sr at 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 at 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 at 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/
>>>
>>> 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.
>
> Seems fine to me. Perhaps we should have dev_get_addr_ptr() to do
> this for us?
Might make sense. I can generate a small patch for this.
Perhaps we should better use "uintptr_t" as type for the intermediate
variable instead. But then we can effectively drop the intermediate
variable and do the casting directly.
What do you think?
Thanks,
Stefan
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