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annotate linux-patch/README @ 121:87b34a244901

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fc-simtool: pb-erase-range command implemented
author Mychaela Falconia <falcon@freecalypso.org>
date Thu, 28 Jan 2021 05:04:16 +0000
parents d7a1e7a6d6ba
children 95c2a67e1219
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Mychaela Falconia <falcon@freecalypso.org>
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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, and the goal of bringing DUART28C
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22 support into mainline Linux is still in limbo as of 2020-12.
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23
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24 Johan (the ftdi_sio driver maintainer who was the target of our initial pressure
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25 campaign to get the needed driver quirk accepted) has now proposed a generalized
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26 version of Mother Mychaela's original idea; this generalized version is just as
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27 good for our purposes because in the end it still recognizes our custom USB ID
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28 and sets the quirk flag which we require, but it also helps other potential
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29 users who may have similar needs, but who work with "any" serial port rather
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30 than a custom USB ID. The current version as of this writing of Johan's patch
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31 series implementing his proposed generalized solution is this one:
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32
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33 https://lore.kernel.org/linux-serial/X8iuCXYhOBVMGvXv@localhost/T/
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34
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35 However, the comments in that thread indicate that the maintainers seem intent
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36 on delaying this integration until 5.12 merge window if not even later, thus we
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37 are still months away from any hope of resolution. Because We The End Users
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38 cannot be expected to put our lives on hold and just sit and wait for kernel
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39 maintainers to get their act together, we need some immediate solution for our
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40 use right now - and the minpatch-* series presented here is our current best
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41 offering for end user purposes.
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42
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43 3 end user patch series versions are presented in minpatch-4.4.14,
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44 minpatch-4.4.240 and minpatch-4.9.240. 4.4.240 and 4.9.240 already include the
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45 preliminary JTAG+UART USB ID code support patch (which serves mainly as an
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46 anchor marking the place where the new DUART28C USB ID code needs to go in
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47 ftdi_sio_ids.h and in the ftdi_sio.c ID code table), but 4.4.14 predates this
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48 patch by a few years, thus minpatch-4.4.14 includes a backport of this
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49 preliminary patch as well. After this preliminary patch, each minpatch-*
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50 version includes the quirk port_probe patch and the main patch adding DUART28C
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51 support with the needed quirk. These latter patches are the closest version we
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52 have to what we are hoping to see eventually merged into mainline, and they have
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53 already undergone rounds of revision in response to maintainer Johan's criticism
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54 - but this "minimal patch" version is limited to just the ftdi_sio driver, not
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55 extending into more generic layers, hence the actual quirk flag is implemented
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56 inside ftdi_sio, not fully generalized like it is in the version which we are
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57 hoping to see merged into mainline in future months/years.