Documentation/i2c/i2c-topology.rst

23 each adapter has a parent adapter (except the root adapter) and zero or
25 I2C transfers, and all adapters with a parent are part of an "i2c-mux"
40 mux-locked or parent-locked muxes.
46 Mux-locked muxes does not lock the entire parent adapter during the
47 full select-transfer-deselect transaction, only the muxes on the parent
50 their tasks. Since the parent adapter is not fully locked during the
72  2. M1 locks muxes on its parent (the root adapter in this case).
75     These transfers are normal I2C transfers that locks the parent
77  5. M1 feeds the I2C transfer from step 1 to its parent adapter as a
78     normal I2C transfer that locks the parent adapter.
81  8. M1 unlocks muxes on its parent.
93   If you build a topology with a mux-locked mux being the parent
94   of a parent-locked mux, this might break the expectation from the
95   parent-locked mux that the root adapter is locked during the
128 Parent-locked muxes lock the parent adapter during the full select-
130 has to ensure that any and all I2C transfers through that parent
140     .--------.     |  parent- |-----| dev D1 |
151  2.  M1 locks muxes on its parent (the root adapter in this case).
152  3.  M1 locks its parent adapter.
158      unlocked I2C transfer, so that it does not deadlock the parent
162  9.  M1 unlocks its parent adapter.
163  10. M1 unlocks muxes on its parent.
171 When using a parent-locked mux, be aware of the following restrictions:
174   If you build a topology with a parent-locked mux being the child
178   and the parent mux issues I2C transfers as part of its select).
179   This is especially the case if the parent mux is mux-locked, but
180   it may also happen if the parent mux is parent-locked.
193 Parent-locked mux as parent of parent-locked mux
199     .--------.     |  parent- |-----|  parent- |-----| dev D1 |
208 the full duration of the operation (both muxes lock their parent,
209 and specifically when M2 requests its parent to lock, M1 passes
217 Mux-locked mux as parent of mux-locked mux
240 Mux-locked mux as parent of parent-locked mux
246     .--------.     |   mux-   |-----|  parent- |-----| dev D1 |
274 Parent-locked mux as parent of mux-locked mux
280     .--------.     |  parent- |-----|   mux-   |-----| dev D1 |
322 Two parent-locked sibling muxes
329                    |  parent- |--'  '--------'
334     .--------.  |  |  parent- |-----| dev D3 |
346 Mux-locked and parent-locked sibling muxes
358     .--------.  |  |  parent- |-----| dev D3 |
374 Whether a device is mux-locked or parent-locked depends on its
381 i2c-mux-gpio              Normally parent-locked, mux-locked iff
384 i2c-mux-gpmux             Normally parent-locked, mux-locked iff
390 i2c-mux-pinctrl           Normally parent-locked, mux-locked iff