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.