On 5/1/23 07:24, Krzysztof Kozlowski wrote:
On 20/04/2023 23:37, Pierre-Louis Bossart wrote:
On 4/20/23 05:16, Krzysztof Kozlowski wrote:
Soundwire devices are supposed to be kept in reset state (powered off) till their probe() or component bind() callbacks. However if they are already powered on, then they might enumerate before the master initializes bus in qcom_swrm_init() leading to occasional errors like:
The problem statement is really hard to follow.
The peripheral can only be enumerated AFTER a) the manager starts the bus clock and transmitting PING frames b) the peripheral detects the sync words for 16 frames in a row. c) the peripheral reports as Attached in the Device0 slot
That sequence holds whether the manager does the enumeration manually or relies on hardware-assisted autoenumeration. This is what the spec requires.
So why can't the bus clock start be controlled by the manager driver, and started once all required initializations are done?
I mean, there's got to be some sort of parent-child hierarchy with manager first, peripheral(s) second, I don't get how these steps could be inverted or race.
qcom-soundwire 6d30000.soundwire-controller: Qualcomm Soundwire controller v2.0.0 Registered wcd938x_codec audio-codec: bound sdw:0:0217:010d:00:4 (ops wcd938x_sdw_component_ops) wcd938x_codec audio-codec: bound sdw:0:0217:010d:00:3 (ops wcd938x_sdw_component_ops) qcom-soundwire 6ad0000.soundwire-controller: swrm_wait_for_wr_fifo_avail err write overflow
The problem primarily lies in Qualcomm Soundwire controller probe() sequence:
- request_threaded_irq()
- sdw_bus_master_add() - which will cause probe() and component bind() of Soundwire devices, e.g. WCD938x codec drivers. Device drivers might already start accessing their registers.
not if the bus clock hasn't started...
- qcom_swrm_init() - which initializes the link/bus and enables interrupts.
if you can move the clock start in 3) then problem solved. Why can't this be done?
Responding to all your three responses: The clock is enabled in this 3. qcom_swrm_init(), so the old code to my knowledge is written exactly how you expect.
However even with stopped clock, the device enumerates at sdw_bus_master_add(), before anything is enabled.
Erm, that's not physically possible...
The peripheral can report as attached and be enumerated by the manager, i.e. assigned a non-zero "Device Number" after the peripheral synchronizes on 16 frames with valid static and dynamic syncwords. That can only happen if there is a clock toggling and PING frames transmitted on the data line.
There's something else at play here.
I also checked the reset values of these registers - clock is off after reset. Assuming of course I look at correct clock registers... but I have only one.
Any access to device registers at (2) above, will fail because link/bus is not yet initialized.
However the fix is not as simple as moving qcom_swrm_init() before sdw_bus_master_add(), because this will cause early interrupt of new slave attached. The interrupt handler expects bus master (ctrl->bus.md) to be allocated, so this would lead to NULL pointer exception.
Rework the init sequence and change the interrupt handler. The correct sequence fixing accessing device registers before link init is now:
- qcom_swrm_init()
- request_threaded_irq()
- sdw_bus_master_add()
which still might cause early interrupts, if Soundwire devices are not in powered off state before their probe. This early interrupt issue is
You'd need to clarify in which step the bus clock starts. In general, you want to clock started last.
Clock is enabled in qcom_swrm_init() step, but as I wrote above, it looks like it does not matter for enumeration.
without a clock you can't have any enumeration.
* from reset by its probe() or bind() function, as a result of* sdw_bus_master_add().* Add a simple check to avoid NULL pointer except on early interrupts.* Note that if this condition happens, the slave device will not be* enumerated. Its driver should be fixed.???
The codec driver is NEVER involved in enumeration.
If the device stays in power down, only the driver bind can bring it on. enumeration won't happen when device is powered down, right?
The codec driver can indeed control the codec power with sideband links - i.e. not with SoundWire but gpios/I2C/SPI, etc. - and it could very well prevent the codec hardware from showing up on the bus until TBD platform-specific criteria are met.
But that's not really taking part in the enumeration process, rather gating the enumeration process.
The only thing a codec driver should do is provide a callback to be notified of a status change for additional initialization, but the enumeration can be done even in the absence of a codec driver.
The proof in the pudding is that you can 'blacklist' a codec driver and bind it later, after the hardware is enumerated. You can even unbind a codec driver and nothing bad will happen (we hardened that sequence last year).
probe != enumeration != initialization for SoundWire codecs.
Probe and enumeration can happen in any order Initialization can only happen after both probe and enumeration happened.
I am speaking here about component_master_ops->bind() callback.
That's on the manager side, I really don't see how this is related to the codec?
* removing Soundwire bus master.*/- if (ctrl->version < SWRM_VERSION_2_0_0)
ctrl->reg_write(ctrl, ctrl->reg_layout[SWRM_REG_INTERRUPT_MASK_ADDR],0);- if (ctrl->mmio)
ctrl->reg_write(ctrl, ctrl->reg_layout[SWRM_REG_INTERRUPT_CPU_EN],0);- cancel_delayed_work_sync(&ctrl->new_slave_work); sdw_bus_master_delete(&ctrl->bus); clk_disable_unprepare(ctrl->hclk);
should the last two be inverted? Keeping a clock running while removing stuff is asking for trouble.
actually it doesn't really matter, if the interrupts are disabled first and you wait for in-flight work to be done. Ignore this comment.
It is a reversed probe(), which is usually correct. Do you expect probe() like:
clk_enable sdw_bus_master_add
it's likely the other way around,
probe(): sdw_bus_master_add clk_enable
assuming that clk_enable() starts the bus - not sure it does based on the answers above.