netdev - Re: [PATCH v2 1/2] net: qrtr: Drop the MHI auto

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Message-ID: <CAFEp6-3mHFYFPS=iakDyWUknDH8z4qOaHwFLuP=Qz1PvYSL_XA@mail.gmail.com>
Date: Thu, 18 Dec 2025 20:09:53 +0100
From: Loic Poulain <loic.poulain@....qualcomm.com>
To: manivannan.sadhasivam@....qualcomm.com
Cc: Jeff Hugo <jeff.hugo@....qualcomm.com>,
        Carl Vanderlip <carl.vanderlip@....qualcomm.com>,
        Oded Gabbay <ogabbay@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Jeff Johnson <jjohnson@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Maxim Kochetkov <fido_max@...ox.ru>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        mhi@...ts.linux.dev, linux-wireless@...r.kernel.org,
        ath11k@...ts.infradead.org, ath12k@...ts.infradead.org,
        netdev@...r.kernel.org, Bjorn Andersson <andersson@...nel.org>,
        Johan Hovold <johan@...nel.org>, Chris Lew <quic_clew@...cinc.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] net: qrtr: Drop the MHI auto_queue feature for
 IPCR DL channels

On Thu, Dec 18, 2025 at 5:51 PM Manivannan Sadhasivam via B4 Relay
<devnull+manivannan.sadhasivam.oss.qualcomm.com@...nel.org> wrote:
>
> From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
>
> 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 <johan@...nel.org>
> Closes: https://lore.kernel.org/linux-arm-msm/ZyTtVdkCCES0lkl4@hovoldconsulting.com
> Suggested-by: Chris Lew <quic_clew@...cinc.com>
> Acked-by: Jeff Johnson <jjohnson@...nel.org> # drivers/net/wireless/ath/...
> Cc: stable@...r.kernel.org
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>

Reviewed-by: Loic Poulain <loic.poulain@....qualcomm.com>