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

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Message-ID: <aO_QMRj4e7zqJw03@smile.fi.intel.com>
Date: Wed, 15 Oct 2025 19:47:45 +0300
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Jean-François Lessard <jefflessard3@...il.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>, linux-kernel@...r.kernel.org,
	Andy Shevchenko <andy@...nel.org>
Subject: Re: [PATCH v2 0/5] auxdisplay: linedisp: support attribute
 attachment to auxdisplay devices

On Thu, Oct 09, 2025 at 07:19:11AM -0400, Jean-François Lessard wrote:
> 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.

Taking no answer as silent agreement, pushed to my review and testing queue, thanks!

If anything, we have time to address / drop / etc.

> 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.

> >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.

-- 
With Best Regards,
Andy Shevchenko