Re: [PATCH 1/8] net: qualcomm: rmnet: fix struct rmnet_map_header

[Subash Abhinov Kasiviswanathan]

> > 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 -
> >
> > BitÂÂÂÂÂÂÂÂÂÂÂÂ 0ÂÂÂÂÂÂÂÂÂÂÂÂ 1ÂÂÂÂÂÂÂÂÂÂ 2-7ÂÂÂÂÂ 8 - 15ÂÂÂÂÂÂÂÂÂÂ 16 
> > - 31
> > FunctionÂÂ Command / DataÂÂ ReservedÂÂÂÂ PadÂÂ Multiplexer IDÂÂÂ 
> > Payload length
> > BitÂÂÂÂÂÂÂÂÂÂÂ 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.

Higher order bit is Command / Data.

> > 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

Can't this bitfields just be used similar to how struct tcphdr &
iphdr are currently defined. That way, you dont have to make
these many changes.

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h 
b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
index 884f1f5..302d1db 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
@@ -40,9 +40,17 @@ enum rmnet_map_commands {
 };

 struct rmnet_map_header {
+#if defined(__LITTLE_ENDIAN_BITFIELD)
        u8  pad_len:6;
        u8  reserved_bit:1;
        u8  cd_bit:1;
+#elif defined (__BIG_ENDIAN_BITFIELD)
+       u8  cd_bit:1;
+       u8  reserved_bit:1;
+       u8  pad_len:6;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
        u8  mux_id;
        __be16 pkt_len;
 }  __aligned(1);


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