[igt-dev] [PATCH i-g-t 2/4] lib/igt_crc: Introduce common place for crc tables and functions
Petri Latvala
petri.latvala at intel.com
Mon Jun 13 06:23:49 UTC 2022
On Mon, Jun 13, 2022 at 08:26:36AM +0300, Petri Latvala wrote:
> On Mon, Jun 13, 2022 at 05:57:02AM +0200, Zbigniew Kempczyński wrote:
> > On Fri, Jun 10, 2022 at 10:53:48AM +0300, Petri Latvala wrote:
> > > On Fri, Jun 10, 2022 at 07:24:39AM +0200, Zbigniew Kempczyński wrote:
> > > > On Thu, Jun 09, 2022 at 12:44:11PM +0300, Petri Latvala wrote:
> > > > > On Tue, Jun 07, 2022 at 07:24:09AM +0200, Zbigniew Kempczyński wrote:
> > > > > > Add crc32 table for on-cpu crc calculation function. Other tables and
> > > > > > algorithms should be added here allowing reuse tables for in-gpu crc
> > > > > > calculation.
> > > > > >
> > > > > > Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
> > > > > > ---
> > > > > > .../igt-gpu-tools/igt-gpu-tools-docs.xml | 1 +
> > > > > > lib/igt_crc.c | 107 ++++++++++++++++++
> > > > > > lib/igt_crc.h | 31 +++++
> > > > > > lib/meson.build | 1 +
> > > > > > 4 files changed, 140 insertions(+)
> > > > > > create mode 100644 lib/igt_crc.c
> > > > > > create mode 100644 lib/igt_crc.h
> > > > > >
> > > > > > diff --git a/docs/reference/igt-gpu-tools/igt-gpu-tools-docs.xml b/docs/reference/igt-gpu-tools/igt-gpu-tools-docs.xml
> > > > > > index 1774256530..b78f1eb6ff 100644
> > > > > > --- a/docs/reference/igt-gpu-tools/igt-gpu-tools-docs.xml
> > > > > > +++ b/docs/reference/igt-gpu-tools/igt-gpu-tools-docs.xml
> > > > > > @@ -22,6 +22,7 @@
> > > > > > <xi:include href="xml/igt_chamelium.xml"/>
> > > > > > <xi:include href="xml/igt_collection.xml"/>
> > > > > > <xi:include href="xml/igt_core.xml"/>
> > > > > > + <xi:include href="xml/igt_crc.xml"/>
> > > > > > <xi:include href="xml/igt_debugfs.xml"/>
> > > > > > <xi:include href="xml/igt_device.xml"/>
> > > > > > <xi:include href="xml/igt_device_scan.xml"/>
> > > > > > diff --git a/lib/igt_crc.c b/lib/igt_crc.c
> > > > > > new file mode 100644
> > > > > > index 0000000000..e634f5cf27
> > > > > > --- /dev/null
> > > > > > +++ b/lib/igt_crc.c
> > > > > > @@ -0,0 +1,107 @@
> > > > > > +/*-
> > > > > > + * COPYRIGHT (C) 1986 Gary S. Brown. You may use this program, or
> > > > > > + * code or tables extracted from it, as desired without restriction.
> > > > > > + */
> > > > > > +
> > > > > > +/*
> > > > > > + * First, the polynomial itself and its table of feedback terms. The
> > > > > > + * polynomial is
> > > > > > + * X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
> > > > > > + *
> > > > > > + * Note that we take it "backwards" and put the highest-order term in
> > > > > > + * the lowest-order bit. The X^32 term is "implied"; the LSB is the
> > > > > > + * X^31 term, etc. The X^0 term (usually shown as "+1") results in
> > > > > > + * the MSB being 1
> > > > > > + *
> > > > > > + * Note that the usual hardware shift register implementation, which
> > > > > > + * is what we're using (we're merely optimizing it by doing eight-bit
> > > > > > + * chunks at a time) shifts bits into the lowest-order term. In our
> > > > > > + * implementation, that means shifting towards the right. Why do we
> > > > > > + * do it this way? Because the calculated CRC must be transmitted in
> > > > > > + * order from highest-order term to lowest-order term. UARTs transmit
> > > > > > + * characters in order from LSB to MSB. By storing the CRC this way
> > > > > > + * we hand it to the UART in the order low-byte to high-byte; the UART
> > > > > > + * sends each low-bit to hight-bit; and the result is transmission bit
> > > > > > + * by bit from highest- to lowest-order term without requiring any bit
> > > > > > + * shuffling on our part. Reception works similarly
> > > > > > + *
> > > > > > + * The feedback terms table consists of 256, 32-bit entries. Notes
> > > > > > + *
> > > > > > + * The table can be generated at runtime if desired; code to do so
> > > > > > + * is shown later. It might not be obvious, but the feedback
> > > > > > + * terms simply represent the results of eight shift/xor opera
> > > > > > + * tions for all combinations of data and CRC register values
> > > > > > + *
> > > > > > + * The values must be right-shifted by eight bits by the "updcrc
> > > > > > + * logic; the shift must be unsigned (bring in zeroes). On some
> > > > > > + * hardware you could probably optimize the shift in assembler by
> > > > > > + * using byte-swap instructions
> > > > > > + * polynomial $edb88320
> > > > >
> > > > > This is also in the original code but... what?
> > > >
> > > > For of writing coefficients:
> > > >
> > > > X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
> > > >
> > > > bin(0xedb88320)
> > > > 0b 1110 1101 1011 1000 1000 0011 0010 0000
> > > > 012 45 7 8 22 23 26
> > > > 10
> > > > 11
> > > > 12 16
> > > >
> > > > Here it is well explained:
> > > > https://www.greenend.org.uk/rjk/tech/crc.html
> > >
> > > Can the last sentence of the comment be restructured to be more
> > > English? In the current form it's like
> >
> > You mean in-code comment or my comment? If above I just copied it 1:1
> > and I would like to keep this intact. If mine I will send this in
> > next version.
>
> The comment in the code.
Meh, everyone who copies the code seems to be just carrying the
comment as is. Might as well do the same here.
--
Petri Latvala
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