Hello Stephen,
On 01/07/2016 07:25 PM, Stephen Warren wrote:
On 01/07/2016 04:40 AM, Przemyslaw Marczak wrote:
The present implementation of __of_translate_address() taken
from the Linux, is designed for translate bus/child address
mappings by using 'ranges' property - and it doesn't allow
for checking an address for a device's node with zero size-cells.
The 'size-cells > 0' is required for bus/child address mapping,
but is not required for non-memory mapped address, e.g.: I2C chip.
Then when we need only raw 'reg' property's value.
Since the I2C device address goes to a single-cell reg property,
support for that case is welcome, but currently calling dev_get_addr()
for I2C device will return 'FDT_ADDR_T_NONE', and print the warning:
warning:
__of_translate_address: Bad cell count for 'some-dev'
This patch takes the wrong approach.
It simply doesn't make sense to /attempt/ to translate an I2C address
into an MMIO address space. It's a nonsensical operation; no such
translation is possible under any circumstances because I2C and MMIO
addresses mean completely different things and simply can't be
translated to each-other.
Rather than making this nonsensical operation succeed in a way that
gives the desired no-op result, the nonsensical operation simply
shouldn't be performed in the first place.
Okay, the example with I2C may be little confusing - I could use some
general naming convention. However, this patch updates FDT-related code
only.
In one of your previous e-mails, you well argued that we shouldn't use
dev_get_reg() for some buses, since they have a different 'reg' meaning.
You are right, using dev_get_addr() as universal function may be
nonsensical.
Please note, that the present implementation of function:
'__of_translate_address()' - allows for 1:1 translation, but only if
'#size-cells' exists. So the below case is possible:
----------------------
parent {
address-cells = <1>;
size-cells = <1>;
reg = <0x10000000 0x1000>;
child {
reg = <0xa00 0x100>;
};
};
dev_get_reg(child) - will return '0xa00'
----------------------
If we don't need the address length, we can define:
----------------------
parent {
address-cells = <1>;
size-cells = <0>;
reg = <0x10000000 0x1000>;
child {
reg = <0xa00>;
};
};
code:
dev_get_reg(child) - returns '0xa00'
----------------------
I would like to distinguish few things:
1. This patch just adds the support for the above second case, which is
sensible and possible from specification point of view.
2. How it will be used by the code - is another thing.
3. If some driver's code can just use of dev_get_addr() for it's case,
then why shouldn't it? Since it, knows how to interpret the returned
value in its own specified way - and also it's described by the proper
binding file, what the reg represents - then I don't threat this as
issue. And here the example may be:
- s5p_gpio.c - exynos GPIO driver
4. If I update the commit message with a general naming convention
(parent/children) instead of using I2C suggestion - will be that patch
acceptable for you?
Best regards,
--
Przemyslaw Marczak
Samsung R&D Institute Poland
Samsung Electronics
p.marc...@samsung.com
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