Re: [PATCH v2 1/2] net: qrtr: Drop the MHI auto_queue feature for IPCR DL channels

On 25-12-18 22:21:44, Manivannan Sadhasivam via B4 Relay wrote:
> From: Manivannan Sadhasivam <[email protected]>
> 
> MHI stack offers the 'auto_queue' feature, which allows the MHI stack to
> auto queue the buffers for the RX path (DL channel). Though this feature
> simplifies the client driver design, it introduces race between the client
> drivers and the MHI stack. For instance, with auto_queue, the 'dl_callback'
> for the DL channel may get called before the client driver is fully probed.
> This means, by the time the dl_callback gets called, the client driver's
> structures might not be initialized, leading to NULL ptr dereference.
> 
> Currently, the drivers have to workaround this issue by initializing the
> internal structures before calling mhi_prepare_for_transfer_autoqueue().
> But even so, there is a chance that the client driver's internal code path
> may call the MHI queue APIs before mhi_prepare_for_transfer_autoqueue() is
> called, leading to similar NULL ptr dereference. This issue has been
> reported on the Qcom X1E80100 CRD machines affecting boot.
> 
> So to properly fix all these races, drop the MHI 'auto_queue' feature
> altogether and let the client driver (QRTR) manage the RX buffers manually.
> In the QRTR driver, queue the RX buffers based on the ring length during
> probe and recycle the buffers in 'dl_callback' once they are consumed. This
> also warrants removing the setting of 'auto_queue' flag from controller
> drivers.
> 
> Currently, this 'auto_queue' feature is only enabled for IPCR DL channel.
> So only the QRTR client driver requires the modification.
> 
> Fixes: 227fee5fc99e ("bus: mhi: core: Add an API for auto queueing buffers for DL channel")
> Fixes: 68a838b84eff ("net: qrtr: start MHI channel after endpoit creation")
> Reported-by: Johan Hovold <[email protected]>
> Closes: https://lore.kernel.org/linux-arm-msm/[email protected]
> Suggested-by: Chris Lew <[email protected]>
> Acked-by: Jeff Johnson <[email protected]> # drivers/net/wireless/ath/...
> Cc: [email protected]
> Signed-off-by: Manivannan Sadhasivam <[email protected]>

Tested on Dell XPS13 9345, so:

Tested-by: Abel Vesa <[email protected]>