Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751930AbdF3Je0 (ORCPT ); Fri, 30 Jun 2017 05:34:26 -0400 Received: from mail.free-electrons.com ([62.4.15.54]:33433 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751565AbdF3JeZ (ORCPT ); Fri, 30 Jun 2017 05:34:25 -0400 Date: Fri, 30 Jun 2017 11:34:22 +0200 From: Maxime Ripard To: Jonathan Liu Cc: David Airlie , Chen-Yu Tsai , linux-kernel , dri-devel , linux-arm-kernel , linux-sunxi Subject: Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus Message-ID: <20170630093422.om7b75q5wyuby6r7@flea> References: <20170627143652.13075-1-net147@gmail.com> <20170628092024.ejxy6itqj3hx6yew@flea> <20170629155620.4keqi4cumbtvv63u@flea> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="aitxfxqh5s552c6a" Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4477 Lines: 114 --aitxfxqh5s552c6a Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, On Fri, Jun 30, 2017 at 08:22:13AM +1000, Jonathan Liu wrote: > Hi Maxime, >=20 > On 30 June 2017 at 01:56, Maxime Ripard > wrote: > > On Wed, Jun 28, 2017 at 08:39:33PM +1000, Jonathan Liu wrote: > >> >> + u32 int_status; > >> >> + u32 fifo_status; > >> >> + /* Read needs empty flag unset, write needs full flag unset */ > >> >> + u32 flag =3D read ? SUN4I_HDMI_DDC_FIFO_STATUS_EMPTY : > >> >> + SUN4I_HDMI_DDC_FIFO_STATUS_FULL; > >> >> + int ret; > >> >> + > >> >> + /* Wait until error or FIFO ready */ > >> >> + ret =3D readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_INT_ST= ATUS_REG, > >> >> + int_status, > >> >> + is_err_status(int_status) || > >> >> + is_fifo_flag_unset(hdmi, &fifo_statu= s, flag), > >> >> + min(len, SUN4I_HDMI_DDC_FIFO_SIZE) *= byte_time, > >> >> + 100000); > >> >> + > >> >> + if (is_err_status(int_status)) > >> >> + return -EIO; > >> >> + if (ret) > >> >> + return -ETIMEDOUT; > >> > > >> > Why not just have > >> > ret =3D readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_FIFO_STATUS_R= EG, reg, > >> > !(reg & flag), 100, 100000); > >> > > >> > if (ret < 0) > >> > if (is_err_status()) > >> > return -EIO; > >> > return ret; > >> > > >> > > >> > >> If I check error status after readl_poll_timeout and there is an error > >> (e.g. the I2C address does not have a corresponding device connected > >> or nothing connected to HDMI port) it will keep checking the fifo > >> status even though error bit is set in the int status and then timeout > >> after 100 ms. If it checks the int status register at the same time, > >> it will error after 100 nanoseconds. I don't want to introduce > >> unnecessary delays considering part of the reason for adding this > >> driver to make it more usable for non-standard use cases. > > > > Well, polling for 100ms doesn't seem great either. What was the > > rationale behind that timeout? > > >=20 > When an error occurs one of the error bits will be set in the > INT_STATUS register so this is detected very quickly if I check the > INT_STATUS and FIFO_STATUS at the same time. The 100 ms timeout is in > case the I2C slave does clock stretching in which case the transfer > may take longer than the predicted time. 100ms isn't stretching anymore, it's worse than that. > > And we can also reverse the check and look at the INT_STATUS > > register. The errors will be there, and we can program the threshold > > we want in both directions and use the > > DDC_FIFO_Request_Interrupt_Status bit. > > >=20 > I did try that when I was doing the v3 patch but I couldn't get it to > work as mentioned previously in the v3 patch discussion. I programmed > the FIFO_RX_TRIGGER_THRES and FIFO_TX_TRIGGER_THRES in DDC_FIFO_Ctrl > register at the same time as setting FIFO_Address_Clear but the > request interrupt status bit did not get updated to the appropriate > state that is consistent with the FIFO level and the thresholds. I did > try this several times for subsequent patch versions without success. What values did you set it to? Maxime --=20 Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com --aitxfxqh5s552c6a Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIcBAEBAgAGBQJZVhseAAoJEBx+YmzsjxAgTjwP/3oJqUtz+fqTaYdytZFAk9WS m64macwdhG8b3Opu3lVCZljPFopAYXSn6S+SaoQ7P1/RCAmggE/ir81tEnSZrJVu YPV4WZddO07Agw23XpLZkoPx2MF3CPPreUDfb8IFb1iRDiTDzAdFrO9cVpfHeD2C mGnwNgnAyyeCqwrmwJeYL449RjXlyyAbhvsoTtYwEWUUWLEm2EmyVos8eGFFzMQ/ EDVD9Lna27GZ3syRjglpF0TBzxX4MdoMZgpHL3Hu1+yap+G5E9x5n5A06brqEjrp 69mC0uIQQ1kqUCByKxR7XNWhCKE+ESIPLrUaOJIc7Zvgv6vMfQ67k3xRU8QZcQ3J RHkmW2SS6CcBt+D3d7ZtgmRM8OaFL74amBymnTDnKyFYNcsurkqFhxPHYlfdS1ZZ L3hwPo5Q1wbWz/c6MtBLQObf+qxU4NWWwhBuVFCJ6p9pBsmMw0dulClMQZFInAv+ gt5iRVfv+OjL7QkHFBJuXaHLSbqkIqmaBMGgwYxyY3q+hxKW+bhQZUSdA/bE5uBx AF6pL9Jb5uMjihLpMz58xv+HEV4XhzmlIZlHa7yjq/ysTHNgeke3lKKV8lF17omj RL2Qb5eoBkj2JH5X0E9p86vr4lxxom7J9LlBeY2kx+XK2TWMNiIVqsD3u1ykPZP3 LdeUMjATUZRB7N6cnBk2 =Zq/h -----END PGP SIGNATURE----- --aitxfxqh5s552c6a--