Re: [PATCH v10] usb: dwc3: debugfs: Resume dwc3 before accessing registers

[Johan Hovold <johan@kernel.org>]

On Tue, May 09, 2023 at 08:18:36PM +0530, Udipto Goswami wrote:
> When the dwc3 device is runtime suspended, various required clocks are in
> disabled state and it is not guaranteed that access to any registers would
> work. Depending on the SoC glue, a register read could be as benign as
> returning 0 or be fatal enough to hang the system.
> 
> In order to prevent such scenarios of fatal errors, make sure to resume
> dwc3 then allow the function to proceed.
> 
> Fixes: 72246da40f37 ("usb: Introduce DesignWare USB3 DRD Driver")
> Cc: stable@vger.kernel.org #3.2: 30332eeefec8: debugfs: regset32: Add Runtime PM support
> Signed-off-by: Udipto Goswami <quic_ugoswami@quicinc.com>
> ---
> v10: Re-wrote the subject & the commit text along with the dependency.
> v9: Fixed function dwc3_rx_fifo_size_show & return values in function
> 	dwc3_link_state_write along with minor changes for code symmetry.
> v8: Replace pm_runtime_get_sync with pm_runtime_resume_and get.
> v7: Replaced pm_runtime_put with pm_runtime_put_sync & returned proper values.
> v6: Added changes to handle get_dync failure appropriately.
> v5: Reworked the patch to resume dwc3 while accessing the registers.
> v4: Introduced pm_runtime_get_if_in_use in order to make sure dwc3 isn't
> 	suspended while accessing the registers.
> v3: Replace pr_err to dev_err. 
> v2: Replaced return 0 with -EINVAL & seq_puts with pr_err.

I've verified that this prevents the system from hanging when accessing
the debugfs interface while the controller is runtime suspended on the
ThinkPad X13s (sc8280xp):

Reviewed-by: Johan Hovold <johan+linaro@kernel.org>
Tested-by: Johan Hovold <johan+linaro@kernel.org>

Johan