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[71.195.29.92]) by smtp.googlemail.com with ESMTPSA id i13sm423199itb.9.2019.05.20.14.23.28 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 May 2019 14:23:30 -0700 (PDT) Subject: Re: [PATCH 1/8] net: qualcomm: rmnet: fix struct rmnet_map_header To: Subash Abhinov Kasiviswanathan Cc: arnd@arndb.de, david.brown@linaro.org, agross@kernel.org, davem@davemloft.net, bjorn.andersson@linaro.org, ilias.apalodimas@linaro.org, cpratapa@codeaurora.org, syadagir@codeaurora.org, evgreen@chromium.org, benchan@google.com, ejcaruso@google.com, netdev@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20190520135354.18628-1-elder@linaro.org> <20190520135354.18628-2-elder@linaro.org> From: Alex Elder Message-ID: <81fd1e01-b8e3-f86a-fcc9-2bcbc51bd679@linaro.org> Date: Mon, 20 May 2019 16:23:28 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/20/19 3:11 PM, Subash Abhinov Kasiviswanathan wrote: > On 2019-05-20 07:53, Alex Elder wrote: >> The C bit-fields in the first byte of the rmnet_map_header structure >> are defined in the wrong order.  The first byte should be formatted >> this way: >>                  +------- reserved_bit >>                  | +----- cd_bit >>                  | | >>                  v v >>     +-----------+-+-+ >>     |  pad_len  |R|C| >>     +-----------+-+-+ >>      7 6 5 4 3 2 1 0  <-- bit position >> >> But the C bit-fields that define the first byte are defined this way: >>     u8 pad_len:6; >>     u8 reserved_bit:1; >>     u8 cd_bit:1; >> > > If the above illustration is supposed to be in network byte order, > then it is wrong. The documentation has the definition for the MAP > packet. Network *bit* order is irrelevant to the host. Host memory is byte addressable only, and bit 0 is the low-order bit. > Packet format - > > Bit             0             1           2-7      8 - 15           16 - 31 > Function   Command / Data   Reserved     Pad   Multiplexer ID    Payload length > Bit            32 - x > Function     Raw  Bytes I don't know how to interpret this. Are you saying that the low- order bit of the first byte is the command/data flag? Or is it the high-order bit of the first byte? I'm saying that what I observed when building the code was that as originally defined, the cd_bit field was the high-order bit (bit 7) of the first byte, which I understand to be wrong. If you are telling me that the command/data flag resides at bit 7 of the first byte, I will update the field masks in a later patch in this series to reflect that. > The driver was written assuming that the host was running ARM64, so > the structs are little endian. (I should have made it compatible > with big and little endian earlier so that is my fault). Little endian and big endian have no bearing on the host's interpretation of bits within a byte. Please clarify. I want the patches to be correct, and what you're explaining doesn't really straighten things out for me. -Alex > In any case, this patch on its own will break the data operation on > ARM64, so it needs to be folded with other patches. > >> And although this isn't portable, I can state that when I build it >> the result puts the bit-fields in the wrong location (e.g., the >> cd_bit is in bit position 7, when it should be position 0). >> >> Fix this by reordering the definitions of these struct members. >> Upcoming patches will reimplement these definitions portably. >> >> Signed-off-by: Alex Elder >> --- >>  drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h | 4 ++-- >>  1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h >> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h >> index 884f1f52dcc2..b1ae9499c0b2 100644 >> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h >> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h >> @@ -40,9 +40,9 @@ enum rmnet_map_commands { >>  }; >> >>  struct rmnet_map_header { >> -    u8  pad_len:6; >> -    u8  reserved_bit:1; >>      u8  cd_bit:1; >> +    u8  reserved_bit:1; >> +    u8  pad_len:6; >>      u8  mux_id; >>      __be16 pkt_len; >>  }  __aligned(1); >