linux-kernel - Re: [PATCH v2 0/5] auxdisplay: linedisp: support attribute attachment to auxdisplay devices

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Message-ID: <88DC2879-1107-47C1-A713-EDA720BB12E8@gmail.com>
Date: Thu, 09 Oct 2025 07:19:11 -0400
From: Jean-François Lessard <jefflessard3@...il.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
CC: linux-kernel@...r.kernel.org, Andy Shevchenko <andy@...nel.org>
Subject: Re: [PATCH v2 0/5] auxdisplay: linedisp: support attribute attachment to auxdisplay devices

Hi Geert,

I hope this message finds you well. I wanted to follow up on this v2
line-display enhancement patch series submitted three weeks ago.

Le 26 septembre 2025 10 h 31 min 16 s HAE, "Jean-François Lessard" <jefflessard3@...il.com> a écrit :
>Le 18 septembre 2025 08 h 13 min 10 s HAE, "Jean-François Lessard" <jefflessard3@...il.com> a écrit :
>>This series modernizes the auxdisplay line display (linedisp) library to
>>enable seamless integration with auxdisplay parent devices while
>>maintaining backward compatibility.
>>
>>The key improvement is adding attach/detach APIs that allow linedisp sysfs
>>attributes to be bound directly to their parent auxdisplay devices avoiding
>>child device proliferation and enabling a uniform 7-segment userspace
>>interface across different driver architectures.
>>
>>This series introduces attachment infrastructure for linedisp devices.
>>The first consumer of this API will be the TM16XX driver series.
>>See the related patch series:
>>  auxdisplay: Add TM16xx 7-segment LED matrix display controllers driver
>>
>>Changes include:
>>1. Encapsulate container_of() usage with to_linedisp() helper function for
>>   cleaner context retrieval
>>2. Improve message display behavior with static padding when message length
>>   is smaller than display width
>>3. Add 'num_chars' read-only attribute for userspace capability discovery
>>4. Add attach/detach API for sysfs attributes binding to parent devices
>>5. Document all linedisp sysfs attributes in ABI documentation
>>
>>All existing linedisp_register() users remain unaffected. The new APIs
>>enable drivers like TM16XX to integrate 7-segment functionality within
>>their LED class device hierarchy while providing a uniform 7-segment API.
>>
>>Thanks to Andy Shevchenko for early feedback and guidance.
>>
>>V1 changelog:
>>- Remove should_scroll() check in linedisp_scroll()
>>- Keep attributes sorted alphabetically
>>- Document, invert logic and rename owns_device to direct
>>- Document linedisp_attach()/_register() must be freed by their
>>  respective APIs after use
>>- Change call order of display default message and add attributes
>>  to prevent racy userspace condition
>>- Separate delete_attachment() call from linedisp variable declaration
>>- Document existing attributes separately, in the first patch
>>
>>RFC changelog:
>>- Replace scope_guard() with guard()() for synchronized list operations.
>>- Replace NULL assignments with proper list_entry_is_head() pattern.
>>- Clearly document why introducing the attach/detach APIs.
>>- Split in patch series, each patch containing a specific change.
>>- Implement static (non-scrolling) display for short messages.
>>- Document exisiting and new ABI sysfs attributes.
>>
>>Jean-François Lessard (5):
>>  docs: ABI: auxdisplay: document linedisp library sysfs attributes
>>  auxdisplay: linedisp: encapsulate container_of usage within
>>    to_linedisp
>>  auxdisplay: linedisp: display static message when length <= display
>>    size
>>  auxdisplay: linedisp: add num_chars sysfs attribute
>>  auxdisplay: linedisp: support attribute attachment to auxdisplay
>>    devices
>>
>> .../ABI/testing/sysfs-auxdisplay-linedisp     |  90 +++++++
>> drivers/auxdisplay/line-display.c             | 240 ++++++++++++++++--
>> drivers/auxdisplay/line-display.h             |   4 +
>> 3 files changed, 312 insertions(+), 22 deletions(-)
>> create mode 100644 Documentation/ABI/testing/sysfs-auxdisplay-linedisp
>>
>
>Hi Andy and Geert,
>
>This is a gentle ping on the v2 line-display enhancement patch series submitted
>over a week ago. I have just submitted v5 of the TM16xx driver series:
>https://lore.kernel.org/linux-devicetree/20250926141913.25919-1-jefflessard3@gmail.com/T/
>
>The TM16xx driver depends on the line-display enhancements for proper
>auxdisplay subsystem integration, as discussed in our previous exchanges. It
>would be great if we could move forward with both patch series together.
>

In the v1 submission, Andy mentioned that the changes look good to him but that
he would wait for your review/Acks before proceeding. The TM16xx driver (v5
recently submitted) depends on these line-display enhancements for proper
auxdisplay subsystem integration.

Would you be able to review the v2 series when you have a chance? Your feedback
would be greatly appreciated so we can move both series forward.

Thank you for your time and consideration.

Best regards,
Jean-François Lessard