Hello Stephen,
On 01/12/2016 05:43 PM, Stephen Warren wrote:
On 01/12/2016 03:25 AM, Przemyslaw Marczak wrote:
Hello Stephen,
On 01/11/2016 05:47 PM, Stephen Warren wrote:
On 01/11/2016 04:21 AM, Przemyslaw Marczak wrote:
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>;
};
};
This case won't ever appear in a correctly written DT where reg
represents an MMIO address; MMIO addresses always have sizes, and
hence
can't have size-cells=0. Hence, translating through a DT
structures like
that is an error case, and shouldn't work.
As we found out, the 'reg' property can represent not only MMIO,
but may
have other meaning,
Of course.
so the above case is possible.
Yes and no.
That DT snippet is certainly possible.
However, that's irrelevant to whether address translation should be
attempted across that boundary. *That* is not legal and should not be
attempted.
Going through your suggestions I took your side.
You are on Cc in the new patchset.
> The 'reg' for the
parent bus can represent MMIO (depends on what its parent defines) and
the child is non-MMIO.
Correct.
You won't allow to use dev_get_addr() for other than MMIO addresses.
Ok, I have no more arguments and no more time.
"You" is incorrect. This has absolutely nothing to do with me, but
rather the rule is imposed by the semantics of device tree.
Also, I never said that dev_get_addr() must not be used for non-MMIO
addresses. In fact, I offered a suggestion to make it work correctly.
What I actually stated is that address translation must not be
attempted
across boundaries between address spaces, since it is semantically
non-sensical.
Ok, please don't take it personally:), it was just how I understood your
opinion.
As you know the specification is not so clean, I thought, that
checking the
existence of "ranges" in parent node - is enough to provide proper
"translation" (or rather choosing the root address space), when
size-cells
== 0. However, checking this condition is probably not enough, but you
didn't provide a device-tree example to give it some light.
Also maybe the translation is a bad word here, since we know that
it's not
MMIO translatable address.
For me, this patch is okay.
If I call it for I2C chip and it returns the chip address in I2C address
space - then I can assume, that this is correct.
Since, at present I2C subsystem takes the 'reg' as property's value, it
looks that there should be no difference when using modified
dev_get_reg().
However the main reason for this change was not I2C code update, but
fixing
Exynos GPIO driver which uses DTB in a quite different way than the
others.
So, I don't need to put the pressure for applying an improvement like
this
one - because it can be fixed in a more proper way.
My issue can be also fixed by removing dev_get_addr() call from Exynos
GPIO driver - so I will do this and within this change, will also
revert
the commit:
"fdt: fix address cell count checking in fdt_translate_address()"
That sounds fine. It'd be better to introduce some code into the I2C
subsystem to handle this, but the approach you mention should work in
practice.
So finally, as you can see at the new patches:
http://patchwork.ozlabs.org/patch/566584/
http://patchwork.ozlabs.org/patch/566587/
I made other quick fix. This should be extended by ranges to be
proper in
100%, but Linux don't use it for this platform and I don't see the
reason
for adding it to U-Boot.
