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annotate linux-patch/README @ 128:95c2a67e1219

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doc, linux-patch: update for failure to mainline DUART28C support
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 02 Feb 2021 04:32:42 +0000
parents d7a1e7a6d6ba
children b8473892b0ce
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1 This directory contains several versions of the Linux kernel ftdi_sio driver
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2 patch that adds support for FreeCalypso DUART28C adapter, i.e., the optional
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3 configuration of DUART28 with boot control outputs.
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4
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5 The version in the orig-202007 directory was produced at the end of 2020-07,
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6 when DUART28 hardware was still being designed; this original version of the
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7 patch was created to test the idea and to prove it working (using a generic
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8 FT2232D board and an oscilloscope), and it was created with the mindset of a
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9 hardware engineer, rather than that of Linux kernel maintainers. This original
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10 patch version was made against kernel version 4.4.14 (the version used by the
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11 Mother), and it predates all later mainline submission and integration attempts.
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12
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13 A patch series against then-current mainline was submitted to ftdi_sio driver
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14 maintainer Johan Hovold in 2020-09 for inclusion in mainline Linux. The
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15 preliminary patch adding support for FreeCalypso JTAG+UART USB ID codes was
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16 readily accepted and has since been propagated to several stable kernel branches
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17 (4.4.240, 4.9.240, 4.14.202, 4.19.152, 5.4.72, 5.8.16, 5.9.1 and mainline 5.10),
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18 but this patch by itself does not help in any way with DUART28C support. The
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19 remaining two patches from the original 2020-09 patch series (a preliminary
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20 patch fixing an oversight in the quirk interface and then the main patch of
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21 interest) were met with resistance, however - please see the article in
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22 doc/Linux-DTR-RTS-flaw for the full explanation. The short version is that
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23 Linux kernel maintainers are refusing to accept our patch on the basis of their
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24 assininity, and thus We The End Users will need to apply this patch locally on
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25 our own systems, probably forever, or at least for the next few billion years
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26 until the Sun swells into a red giant and engulfs the Earth.
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27
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28 3 end user patch series versions are presented in minpatch-4.4.14,
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29 minpatch-4.4.240 and minpatch-4.9.240. 4.4.240 and 4.9.240 already include the
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30 preliminary JTAG+UART USB ID code support patch (which serves mainly as an
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31 anchor marking the place where the new DUART28C USB ID code needs to go in
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32 ftdi_sio_ids.h and in the ftdi_sio.c ID code table), but 4.4.14 predates this
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33 patch by a few years, thus minpatch-4.4.14 includes a backport of this
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34 preliminary patch as well. After this preliminary patch, each minpatch-*
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35 version includes the quirk port_probe patch and the main patch adding DUART28C
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36 support with the needed quirk. These latter patches are the closest version we
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37 ever got to a mainline-acceptable state: they already underwent rounds of
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38 revision in response to the maintainer's criticism, addressing and fixing
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39 various nitpick issues before the whole idea got shot down on more ideological
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40 grounds.