linux-kernel - Re: [PATCH v2 1/3] PCI: Relaxed tail alignment should never increase min

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Message-ID: <b3018c24-7626-d406-2487-67ea32bd2712@linux.intel.com>
Date: Thu, 21 Aug 2025 18:24:12 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Bjorn Helgaas <helgaas@...nel.org>
cc: linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>, 
    Krzysztof Wilczyński <kw@...ux.com>, 
    Tudor Ambarus <tudor.ambarus@...aro.org>, Rio <rio@....me>, 
    D Scott Phillips <scott@...amperecomputing.com>, 
    LKML <linux-kernel@...r.kernel.org>, 
    Christian König <christian.koenig@....com>, 
    stable@...r.kernel.org
Subject: Re: [PATCH v2 1/3] PCI: Relaxed tail alignment should never increase
 min_align

On Thu, 21 Aug 2025, Ilpo Järvinen wrote:

> On Thu, 21 Aug 2025, Bjorn Helgaas wrote:
> 
> > On Mon, Jun 30, 2025 at 05:26:39PM +0300, Ilpo Järvinen wrote:
> > > When using relaxed tail alignment for the bridge window,
> > > pbus_size_mem() also tries to minimize min_align, which can under
> > > certain scenarios end up increasing min_align from that found by
> > > calculate_mem_align().
> > > 
> > > Ensure min_align is not increased by the relaxed tail alignment.
> > > 
> > > Eventually, it would be better to add calculate_relaxed_head_align()
> > > similar to calculate_mem_align() which finds out what alignment can be
> > > used for the head without introducing any gaps into the bridge window
> > > to give flexibility on head address too. But that looks relatively
> > > complex algorithm so it requires much more testing than fixing the
> > > immediate problem causing a regression.
> > > 
> > > Fixes: 67f9085596ee ("PCI: Allow relaxed bridge window tail sizing for optional resources")
> > > Reported-by: Rio <rio@....me>
> > 
> > Was there a regression report URL we could include here?
> 
> There's the Lore thread only:
> 
> https://lore.kernel.org/all/o2bL8MtD_40-lf8GlslTw-AZpUPzm8nmfCnJKvS8RQ3NOzOW1uq1dVCEfRpUjJ2i7G2WjfQhk2IWZ7oGp-7G-jXN4qOdtnyOcjRR0PZWK5I=@r26.me/
> 
> (It's so far back that if there was something else, I've forgotten them 
> by now but looking at the exchanges in the thread, it doesn't look like 
> bugzilla entry or so made out of it.)

Making it "official" tag in case that's easier for you to handle 
automatically...

Link: https://lore.kernel.org/all/o2bL8MtD_40-lf8GlslTw-AZpUPzm8nmfCnJKvS8RQ3NOzOW1uq1dVCEfRpUjJ2i7G2WjfQhk2IWZ7oGp-7G-jXN4qOdtnyOcjRR0PZWK5I=@r26.me/


-- 
 i.