From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Brown Subject: Re: [PATCH] ASoC: ssm2602: Fix ADC powerup sequencing Date: Fri, 25 May 2018 18:24:41 +0100 Message-ID: <20180525172441.GN4828@sirena.org.uk> References: <20180517133009.26079-1-m.felsch@pengutronix.de> <1526640409.3948.5.camel@pengutronix.de> <20180523165352.GA6187@rob-hp-laptop> <20180525094724.3f4edofopk52i3v6@pengutronix.de> <20180525102609.GK4828@sirena.org.uk> <20180525114253.jj6akdazsbxqkbfu@pengutronix.de> <20180525145245.GM4828@sirena.org.uk> <1527261489.4938.9.camel@pengutronix.de> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1939452328822749507==" Return-path: In-Reply-To: <1527261489.4938.9.camel@pengutronix.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: Philipp Zabel Cc: Mark Rutland , Rob Herring , Linux-ALSA , Lars-Peter Clausen , devicetree@vger.kernel.org, Sascha Hauer , Marco Felsch , Liam Girdwood , kernel@pengutronix.de List-Id: devicetree@vger.kernel.org --===============1939452328822749507== Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="8QM4kKE+nfbBA4vJ" Content-Disposition: inline --8QM4kKE+nfbBA4vJ Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, May 25, 2018 at 05:18:09PM +0200, Philipp Zabel wrote: > On Fri, 2018-05-25 at 15:52 +0100, Mark Brown wrote: > > On Fri, May 25, 2018 at 01:42:53PM +0200, Marco Felsch wrote: > > > Also the formula for the delay time (t =3D C =D7 25,000/3.5) depends = only on > > > the capacity size. > > Why not just have the user specify the capacitance of the capacitor on > > the rail which they can directly read from the schematic rather than > > forcing them to do the calcualtion? That seems a bit clearer and more > > user friendly (plus if someone decides the spec was wrong it's easier to > > roll out fixes). > The exact capacitance may not be known or vary above the nominal value > because of cheap components, and the formula from the datasheet is just > a guideline. That variability is going to apply just as much to the charge time calculations/measurements as it is to the initial capacitance value - the results are going to be very much garbage in, garbage out. > I'd expect the usual method to set this delay to be semi-empirical: > "start from the value calculated from datasheet and schematics and then > increase until no more audio artifacts on a representative sample of > boards". > I think it is be better to specify a delay that works than a bogus > capacitance value that happens to correspond to a delay that works. If this is varying so drastically per board/system that it's relevant then we're already into problematic territory. For most devices we just have a number for the part, not something that varies so wildly that each system needs to configure it. --8QM4kKE+nfbBA4vJ Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAlsIRtgACgkQJNaLcl1U h9Bgxwf/RY7Q7a3jCjohxDoR84MqXn+NSDeTJGvqhQ896V5jKPDaH5DmMHm0sNd6 LVybEi3zgb3+y3zXfLKoo4P62Hl83LJZCpQWp0sH5f2TiRPsO2sgKZfXRC93ihZP INUMx031TOZMl3BLPWGCer+wT7QZzHgJY4P/WP0iATZdps6Z8TfxBa30DZ4KRmwr K+HBFhjj4NyQYpFI5uLrRs7utFTWgNh+LS5y8K4YYflIP+nb61FxKwpG5yyeYRGX EIBF1bnJOzJxk1ur9kcWKQ4resM6biY6/eKXu2IMZUpGpfeiCtm+pO6aa5u2HEP4 TtJVkuVZ/9jebSz+AcDafamypcJeng== =RnHn -----END PGP SIGNATURE----- --8QM4kKE+nfbBA4vJ-- --===============1939452328822749507== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline --===============1939452328822749507==--