Hi Przymyslaw,
On 15 January 2016 at 09:35, Stephen Warren swarren@wwwdotorg.org wrote:
On 01/15/2016 03:41 AM, Przemyslaw Marczak wrote:
Hello Simon,
On 01/14/2016 06:17 PM, Simon Glass wrote:
Hi Przemyslaw, Stephen,
On 13 January 2016 at 04:10, Przemyslaw Marczak p.marczak@samsung.com wrote:
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.
You could presumably add it to Linux also.
Thank you both for figuring this out.
Regards, Simon
The commit updates files, which exists in U-Boot only.
Moreover, the problematic reg properties are not used by Linux's Exynos GPIO driver - because all required addresses are hardcoded in the driver. So I don't see the reason for doing it there.
There should only be one definition of DT bindings. That is, both U-Boot and Linux must use the same bindings and hence interpret the DT in the same way. That's the entire point of DT.
Preferably both Linux and U-Boot will use the exact same DT content. There may be some differences, e.g. if U-Boot doesn't support a particular driver/feature, then the nodes/properties that enable that feature can be omitted from the U-Boot DT since they won't be used. However, where the same node/property exists in both places, it should be identical between both.
Prior to proposing any DT changes for U-Boot, the best approach is to get them into the Linux kernel DTs so that they get widespread review against the binding definitions and so that everyone using DT approves the changes.
What would you like to do here?
Regards, Simon