linux-kernel - Re: [PATCH v5 0/3] soc: qcom: extend interface for big endian support

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Message-ID: <aXCrxXvHCUhvhONe@FUE-ALEWI-WINX>
Date: Wed, 21 Jan 2026 11:34:45 +0100
From: Alexander Wilhelm <alexander.wilhelm@...termo.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: David Heidelberg <david@...t.cz>, Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/3] soc: qcom: extend interface for big endian support

On Wed, Jan 21, 2026 at 11:27:35AM +0200, Dmitry Baryshkov wrote:
> On Wed, Jan 21, 2026 at 10:07:22AM +0100, Alexander Wilhelm wrote:
> > On Wed, Jan 21, 2026 at 09:22:07AM +0100, David Heidelberg wrote:
> > > On 19/11/2025 11:40, Alexander Wilhelm wrote:
> > > > Currently, the QMI interface only works on little endian systems due to how
> > > > it encodes and decodes data. Most QMI related data structures are defined
> > > > in CPU native order and do not use endian specific types.
> > > > 
> > > > Add support for endian conversion of basic element types in the QMI
> > > > encoding and decoding logic. Fix the handling of QMI_DATA_LEN fields to
> > > > ensure correct interpretation on big endian systems. These changes are
> > > > required to allow QMI to operate correctly across architectures with
> > > > different endianness.
> > > > ---
> > > 
> > > Hello,
> > > 
> > > I recently (next-20260119) started receiving errors on Pixel 3:
> > > 
> > > [   21.158943] ipa 1e40000.ipa: received modem running event
> > > [   21.164616] qmi_encode: Invalid data length
> > > [   21.168930] qcom_q6v5_pas remoteproc-adsp: failed to send subsystem event
> > > [   21.175844] qmi_encode: Invalid data length
> > > [   21.180494] qcom_q6v5_pas remoteproc-cdsp: failed to send subsystem event
> > > [   21.187467] qmi_encode: Invalid data length
> > > [   21.191772] qcom-q6v5-mss 4080000.remoteproc: failed to send subsystem
> > > event
> > > [   21.199088] qmi_encode: Invalid data length
> > > [   21.203360] qcom-q6v5-mss 4080000.remoteproc: failed to send subsystem
> > > event
> > > [   21.210636] remoteproc remoteproc0: remote processor 4080000.remoteproc
> > > is now up
> > > 
> > > Since it's not well tested, I believe there could be problem with
> > > configuration, but after reverting this series, no errors pop up.
> > > 
> > > I would believe maybe these errors was previously hidden, but just to be
> > > sure asking here.
> > 
> > Hi David,
> > 
> > This is exactly the problem I was afraid of. When the endianness fixes for
> > `ath12k` were rejected, I implemented them in the QMI subsystem instead. I only
> > tested this with `ath11k` and `ath12k` drivers, both on little-endian and
> > big-endian platforms. However, other devices, such as your modem, also rely on
> > QMI, but were not tested.
> > 
> > The difference now is that, instead of using memcpy, basic elements like `u8`,
> > `u16`, `u32`, and `u64` are handled explicitly in separate switch-cases. This
> > raises the question of what exactly the modem and its corresponding driver are
> > doing at this point. Could you please tell me which repository you are working
> > on? I could not find `next-20260119` in either the `ath` or the `stable`
> > repositories.
> 
> https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/?h=next-20260119__;!!I9LPvj3b!AWVWfTEAVZO1j_Z284kxYiMwiOLbmHWEDT8S0RRsUl2rXclrmeyzh9ChVTTXMlhjPLcoRAiuS7Zfx9c0ejF_6IDNCNmVGYaDZmw95gOh$ 

Thanks, Dmitry.

@David:
OK, this is interesting. The QMI subsystem supports exactly the
basic element types from u8 to u64. In your output, I don’t see any errors
like “Unrecognized element size”. Therefore, I assume that the modem is
adhering correctly to the QMI protocol conventions.

The “Invalid data length” error can only occur if `data_len_value <= 0` or
if `temp_ei->elem_len < data_len_value`. However, my changes should not
affect this. Since you are using a Pixel 3, I assume this is a
little-endian platform. Even if your modem performs any endian swapping
internally, this should not affect you.

Unfortunately, I must have overlooked something, I can’t identify the
problem just by reading the code. Without having access to the specific
modem, I’m also unable to debug this properly. As a fallback, you could
revert the changes and drop big-endian support for now. At the moment, I
can’t provide an alternative solution on short notice.


Best regards
Alexander Wilhelm