[Buildroot] [Bug 10171] New: devmem2 w (word) is 8 bytes in x86 64 systems

[Buildroot] [Bug 10171] New: devmem2 w (word) is 8 bytes in x86 64 systems

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10171

            Bug ID: 10171
           Summary: devmem2 w (word) is 8 bytes in x86 64 systems
           Product: buildroot
           Version: unspecified
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: Other
          Assignee: unassigned at buildroot.uclibc.org
          Reporter: ciro.santilli at gmail.com
                CC: buildroot at uclibc.org
  Target Milestone: ---

http://free-electrons.com/pub/mirror/devmem2.c

w maps to unsigned long

Let's use uintX_t for all accesses, and introduce q (quadword) for 64 bit

Specially unintuitive since h (half-word) maps to short int, which in x86_64 is
2 bytes, and thus not half of word.

Also can we move the .c source into the buildroot tree itself in the same
directory as the .mk, since it is so tiny. Or create a separate official git
repo for it.

I'll send patch if you agree.

Like this:
https://github.com/cirosantilli/linux-kernel-module-cheat/blob/d871c008fbf0832e502f8ae1367ecf8ab6796aa5/kernel_module/user/devmem3.c

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[Buildroot] [Bug 10171] devmem2 w (word) is 8 bytes in x86 64 systems

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10171

--- Comment #1 from Matt Weber <matthew.weber@rockwellcollins.com> ---
FYI, the busybox version of devmem is the most up to date and supports quadword
access.  This app I believe is just for backwards compatibility and there are
other address casting address issues with 32bit access on a 64bit bus (like on
the SoC FPGA ARM processors) with this tool.  Maybe a note should be added to
the package to reflect it's in a partially depreciated state?  Or we should
remove it and make it a virtual package setting the busybox option to enabled?

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[Buildroot] [Bug 10171] devmem2 w (word) is 8 bytes in x86 64 systems

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10171

--- Comment #2 from Ciro Santilli <ciro.santilli@gmail.com> ---
Thanks! I didn't know busybox had devmem2. And that one use uintX_t types
already.

The devmem2 package should be deprecated if possible.

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[Buildroot] [Bug 10171] devmem2 w (word) is 8 bytes in x86 64 systems

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10171

Carlos Santos <unixmania@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at buildroot.uclibc |unixmania at gmail.com
                   |.org                        |

--- Comment #3 from Carlos Santos <unixmania@gmail.com> ---
I'm taking this one.

This bug has been frozen for two years. I think we could simply replace devmem2
by a shell script that invokes the busybox devmem utility, mapping the 'type'
argument to the corresponding 'width' one, keeping backward compatibility:

   b -> 8
   h -> 16
   w -> 32

Do you agree?

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[Buildroot] [Bug 10171] devmem2 w (word) is 8 bytes in x86 64 systems

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10171

--- Comment #4 from Ciro Santilli <ciro.santilli@gmail.com> ---
busybox 1.17.2 has:

Usage: devmem ADDRESS [WIDTH [VALUE]]

Read/write from physical address

        ADDRESS Address to act upon
        WIDTH   Width (8/16/...)
        VALUE   Data to be written

I forgot the original motivation, but I think this covers it?

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[Buildroot] [Bug 10171] devmem2 w (word) is 8 bytes in x86 64 systems

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10171

--- Comment #5 from Carlos Santos <unixmania@gmail.com> ---
(In reply to Ciro Santilli from comment #4)

I found that ti-gfx contains a script using devmem2 and submitted a patch to
remove the dependency: https://patchwork.ozlabs.org/patch/1145451/

There are still 8 board configurations that select devmem2, for reasons that I
don't know:

  - at91sam9x5ek_dev_defconfig
  - at91sam9x5ek_mmc_dev_defconfig
  - atmel_sama5d27_som1_ek_mmc_dev_defconfig
  - atmel_sama5d2_xplained_mmc_dev_defconfig
  - atmel_sama5d3_xplained_dev_defconfig
  - atmel_sama5d3_xplained_mmc_dev_defconfig
  - atmel_sama5d4_xplained_dev_defconfig
  - atmel_sama5d4_xplained_mmc_dev_defconfig

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[Buildroot] [Bug 10171] devmem2 w (word) is 8 bytes in x86 64 systems

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10171

--- Comment #6 from Thomas Petazzoni <thomas.petazzoni@free-electrons.com> ---
Thanks Carlos for taking care of the issue. It certainly makes sense to use the
devmem applet from Busybox, when Busybox is enabled.

However, I'm wondering if it makes sense to keep a standalone version of this
program. Most (all?) applets provided by Busybox also have a counterpart
"full-blown" version, which can be useful in situations where Busybox is not
used.

Overall, it feels like this bug is not really a Buildroot bug: it's an upstream
devmem2 bug, which should be reported to upstream and not to Buildroot.

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[Buildroot] [Bug 10171] devmem2 w (word) is 8 bytes in x86 64 systems

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10171

--- Comment #7 from Carlos Santos <unixmania@gmail.com> ---
(In reply to Thomas Petazzoni from comment #6)

Considering that devmem2 is abandoneware and that after commits 2f6e3eae55 and
559856480b6 it is not used by any package or board in Buildroot I think we can
either leave it as is or simply drop the package. It can be resurrected later,
if necessary.

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[Buildroot] [Bug 10171] devmem2 w (word) is 8 bytes in x86 64 systems

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10171

Thomas Petazzoni <thomas.petazzoni@free-electrons.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #8 from Thomas Petazzoni <thomas.petazzoni@free-electrons.com> ---
Fixed by
https://git.buildroot.org/buildroot/commit/?id=2b2579afebfc7a9b8a458af1f2d206101fbfa19c.

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