| Message ID | 20200220172403.26062-1-wsa+renesas@sang-engineering.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | i2c: of: reserve unknown and ancillary addresses | expand |
Hi Wolfram, On Thu, Feb 20, 2020 at 6:26 PM Wolfram Sang <wsa+renesas@sang-engineering.com> wrote: > One outcome of my dynamic address assignment RFC series[1] was that we > need a way to describe an I2C bus in DT fully. This includes unknown > devices and devices requiring multiple addresses. This series implements > that. > > Patches 1+2 do some preparational refactoring. After patch 3, we can > have child nodes with an address, but no compatible. Those addresses > will be marked busy now. They are handled by the dummy driver as well, > but named "reserved" instead of dummy. Patches 4+5 are again some > preparational refactoring. After patch 6, all addresses in a 'reg' array > are now blocked by the I2C core, also using the dummy driver but named > "reserved". So, we can have something like this: > > dummy@13 { Hence should that be "reserved@13"? > reg = <0x13>, <0x14>; > }; Gr{oetje,eeting}s, Geert
One outcome of my dynamic address assignment RFC series[1] was that we need a way to describe an I2C bus in DT fully. This includes unknown devices and devices requiring multiple addresses. This series implements that. Patches 1+2 do some preparational refactoring. After patch 3, we can have child nodes with an address, but no compatible. Those addresses will be marked busy now. They are handled by the dummy driver as well, but named "reserved" instead of dummy. Patches 4+5 are again some preparational refactoring. After patch 6, all addresses in a 'reg' array are now blocked by the I2C core, also using the dummy driver but named "reserved". So, we can have something like this: dummy@13 { reg = <0x13>, <0x14>; }; After patch 7 then, i2c_new_ancillary_device is spiced up to look for such a reserved address and return it as a good-old "dummy" device. Sanity checks include that only a sibling from the same DT node can request such an ancillary address. Stealing addresses from other drivers is not possible anymore. This is something I envisioned for some time now and I am quite happy with the implementation and how things work There is only one thing giving me some headache now. There is a danger of a regression maybe. If someone has multiple 'reg' entries in the DT but never used i2c_new_ancillary_device but i2c_new_dummy_device, then things will break now because i2c_new_dummy_device has not enough information to convert a "reserved" device to a "dummy" one. It will just see the address as busy. However, all binding documentations I found which use 'reg' as an array correctly use i2c_new_ancillary_device. On the other hand, my search strategy for finding such bindings and DTs do not feel perfect to me. Maybe there are also some more corner cases in this area, so this series is still RFC. And some more documentation is needed. Before that, though, the generic I2C binding docs need some overhaul, too. All tested on a Renesas Lager board (R-Car H2). A git branch can be found here: git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git renesas/topic/i2c_alias_device_v2 The I3C list is on CC not only because there is 1-line change in their subsystem, but maybe also because they need to be aware of these changes for their I2C fallback? I don't really know, let me know if you are not interested. Looking forward to comments! Happy hacking, Wolfram [1] https://www.spinics.net/lists/linux-i2c/msg43291.html Wolfram Sang (7): i2c: add sanity check for parameter of i2c_verify_client() i2c: use DEFINE for the dummy driver name i2c: allow DT nodes without 'compatible' i2c: of: remove superfluous parameter from exported function i2c: of: error message unification i2c: of: mark a whole array of regs as reserved i2c: core: hand over reserved devices when requesting ancillary addresses .../devicetree/bindings/i2c/i2c-ocores.txt | 1 - Documentation/devicetree/bindings/i2c/i2c.txt | 4 +- drivers/i2c/i2c-core-base.c | 29 +++++-- drivers/i2c/i2c-core-of.c | 86 +++++++++++-------- drivers/i2c/i2c-core.h | 3 + drivers/i3c/master.c | 2 +- include/linux/i2c.h | 6 +- 7 files changed, 83 insertions(+), 48 deletions(-)