Date: Mon, 20 Jul 2015 18:26:27 +0100
From: Mark Brown <broonie@kernel.org>
To: Alexander Stein <alexander.stein@systec-electronic.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Message-ID: <20150720172627.GF11162@sirena.org.uk>
References: <1437061732-21018-1-git-send-email-alexander.stein@systec-electronic.com>
 <20150716190657.GA11162@sirena.org.uk>
 <3879923.hy2mOjvtRz@ws-stein>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
	protocol="application/pgp-signature"; boundary="ufKotkMdkVlnDasC"
Content-Disposition: inline
In-Reply-To: <3879923.hy2mOjvtRz@ws-stein>
User-Agent: Mutt/1.5.23 (2014-03-12)
Subject: Re: [PATCH 1/1] regmap: regcache-rbtree: Use GFP_ATOMIC when using
 spinlocks
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2624
Lines: 63


--ufKotkMdkVlnDasC
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

On Mon, Jul 20, 2015 at 09:04:05AM +0200, Alexander Stein wrote:
> On Thursday 16 July 2015 20:06:57, Mark Brown wrote:

Please fix your mailer to word wrap within paragraphs for legibility.

> > The expectation here is that we should either be using no or a flat
> > cache here or (if we're using rbtree) providing register defaults to
> > ensure that we never do allocations in the spinlock.  The rbtree code is
> > written on the assumption that we only have to be faster than reading
> > from a serial bus so I'd be worried about it not behaving at all nicely
> > in a spinlock even ignoring this issue.

> AFAICS even a flat cache seems also only be usefull when providing
> defaults, no? (Or having volatile registers).

Well, it's *better* to provide defaults since otherwise everything
defaults to 0 but it does avoid the whole allocation during fast path
issue since it allocates the cache on init and perhaps that's OK.

> So how to handle this properly? Bail out, if fast_io is available and
> cache_type != (REGCACHE_NONE || REGCACHE_FLAT)?

Or perhaps just if we have to do an allocation?  I can see that someone
might want to use an rbtree and would be careful enough to do the init,
though I *am* a bit dubious about it.

> > Why are you using a dynamically allocated rbtree for a device like this?

> On my way home, I came to the same question. In fact this is not a
> driver written by myself, but from here
> http://git.freescale.com/git/cgit.cgi/ppc/sdk/linux.git/tree/drivers/video/fsl-dcu-fb.c#n1024.
> I guess as this is a mmio device and things like regcache_cache_only()
> are used, REGCACHE_FLAT seems appropriate.

Ah, out of tree BSP code...

--ufKotkMdkVlnDasC
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2

iQEcBAEBCAAGBQJVrS9CAAoJECTWi3JdVIfQ38oH/R4P0Kx9hoVP2DbA4X7VH1sT
HV205BUFTYgcx5iZixci+Sxyur0dAE+FzVyZBRn6kmJQ5hEeQrHh+o6HrNcDjc9m
WLY8G45dXYdmtC3mFexVRcHeU5HWzLgVmNeGdV55pAYlfv+eWHzSgtTEU9i/fjgP
ys0ZSHZBD+PQzKhgekKJov/zP5mV0Bg08VrqJx8ohdjIi+ecJiZkWu1KvAkW3TRf
4qbiDokm8mzAUu/3h/dSm0jZZzZeYmCdaXh8MTYU/SFEfsT18NsyolJ/jy+ccGaT
FIkrddxrGXVxx39q9wWxJ32FvThwPiovwWhVrHJ47yqfhilL+XdK1211x/EHBm0=
=fBYn
-----END PGP SIGNATURE-----

--ufKotkMdkVlnDasC--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/