From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jani Nikula Subject: Re: [PATCH v2] drm/i915: Try EDID bitbanging on HDMI after failed read Date: Wed, 03 Jan 2018 09:14:47 +0200 Message-ID: <87vagj2z2w.fsf@intel.com> References: <20180102191218.53beopvnxsg2etmg@intel.com> <151492106622.21495.250228197580562391@mail.alporthouse.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <151492106622.21495.250228197580562391@mail.alporthouse.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" To: Chris Wilson , Rodrigo Vivi , Stefan =?utf-8?Q?Br=C3=BCns?= Cc: David Airlie , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org List-Id: dri-devel@lists.freedesktop.org T24gVHVlLCAwMiBKYW4gMjAxOCwgQ2hyaXMgV2lsc29uIDxjaHJpc0BjaHJpcy13aWxzb24uY28u dWs+IHdyb3RlOgo+IFF1b3RpbmcgUm9kcmlnbyBWaXZpICgyMDE4LTAxLTAyIDE5OjEyOjE4KQo+ PiBPbiBTdW4sIERlYyAzMSwgMjAxNyBhdCAxMDozNDo1NFBNICswMDAwLCBTdGVmYW4gQnLDvG5z IHdyb3RlOgo+PiA+ICsgICAgIGVkaWQgPSBkcm1fZ2V0X2VkaWQoY29ubmVjdG9yLCBpMmMpOwo+ PiA+ICsKPj4gPiArICAgICBpZiAoIWVkaWQgJiYgIWludGVsX2dtYnVzX2lzX2ZvcmNlZF9iaXQo aTJjKSkgewo+PiA+ICsgICAgICAgICAgICAgRFJNX0RFQlVHX0tNUygiSERNSSBHTUJVUyBFRElE IHJlYWQgZmFpbGVkLCByZXRyeSB1c2luZyBHUElPIGJpdC1iYW5naW5nXG4iKTsKPj4gPiArICAg ICAgICAgICAgIGludGVsX2dtYnVzX2ZvcmNlX2JpdChpMmMsIHRydWUpOwo+PiA+ICsgICAgICAg ICAgICAgZWRpZCA9IGRybV9nZXRfZWRpZChjb25uZWN0b3IsIGkyYyk7Cj4+ID4gKyAgICAgICAg ICAgICBpbnRlbF9nbWJ1c19mb3JjZV9iaXQoaTJjLCBmYWxzZSk7Cj4+ID4gKyAgICAgfQo+PiAK Pj4gQXBwcm9hY2ggc2VlbXMgZmluZSBmb3IgdGhpcyBjYXNlLgo+PiBJIGp1c3Qgd29uZGVyIHdo YXQgd291bGQgYmUgdGhlIHJpc2tzIG9mIGZvcmNpbmcgdGhpcyBiaXQgYW5kIGVkaWQgcmVhZCB3 aGVuIG5vdGhpbmcgaXMgcHJlc2VudCBvbiB0aGUgb3RoZXIgZW5kPwo+Cj4gU2hvdWxkIGJlIG5v IG1vcmUgcmlza3kgdGhhbiB1c2luZyBHTUJVUyBhcyB0aGUgYml0LWJhbmdpbmcgaXMgdGhlCj4g dW5kZXJseWluZyBIVyBwcm90b2NvbDsgaXQgc2hvdWxkIGp1c3QgYmUgYWRkaW5nIGFuIGV4dHJh IGRlbGF5IHRvCj4gdGhlIGRpc2Nvbm5lY3RlZCBwcm9iZS4gT2Zmc2V0IGFnYWluc3QgdGhlIGNo YW5jZSB0aGF0IGl0IGZpeGVzCj4gZGV0ZWN0aW9uIG9mIGJvcmRlcmxpbmUgZGV2aWNlcy4KPgo+ IEkgd291bGQgc2F5IHRoYXQgZ2l2ZW4gdGhlIGV4cGxhbmF0aW9uIGFib3ZlLCB0aGUgcXVlc3Rp b24gaXMgd2h5IG5vdAo+IGFwcGx5IGl0IHVuaXZlcnNhbGx5PyAoQm9udXMgcG9pbnRzIGZvciBp bmNsdWRpbmcgdGhlIGV4cGxhbmF0aW9uIGFzCj4gY29tbWVudHMuKQoKSSdtIHdvbmRlcmluZywg aXMgZ21idXMgdG9vIGZhc3QgZm9yIHRoZSBhZGFwdGVycywgZG9lcyBnbWJ1cyBnZW5lcmFsbHkK aGF2ZSBkaWZmZXJlbnQgdGltaW5nIGZvciB0aGUgYWNrL25hayBhcyBkZXNjcmliZWQgaW4gdGhl IGNvbW1pdCBtZXNzYWdlCnRoYW4gYml0IGJhbmdpbmcsIG9yIGFyZSB0aGUgYWRhcHRlcnMganVz dCBwbGFpbiBidWdneT8gRG8gd2UgaGF2ZSBhbnkKY29udHJvbCBvdmVyIGdtYnVzIHRpbWluZ3Mg KGRvbid0IGhhdmUgdGhlIHRpbWUgdG8gcGVydXNlIHRoZSBicHNlYyBqdXN0Cm5vdyk/CgpCUiwK SmFuaS4KCj4gLUNocmlzCj4gX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX18KPiBJbnRlbC1nZnggbWFpbGluZyBsaXN0Cj4gSW50ZWwtZ2Z4QGxpc3RzLmZyZWVk ZXNrdG9wLm9yZwo+IGh0dHBzOi8vbGlzdHMuZnJlZWRlc2t0b3Aub3JnL21haWxtYW4vbGlzdGlu Zm8vaW50ZWwtZ2Z4CgotLSAKSmFuaSBOaWt1bGEsIEludGVsIE9wZW4gU291cmNlIFRlY2hub2xv Z3kgQ2VudGVyCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f CkludGVsLWdmeCBtYWlsaW5nIGxpc3QKSW50ZWwtZ2Z4QGxpc3RzLmZyZWVkZXNrdG9wLm9yZwpo dHRwczovL2xpc3RzLmZyZWVkZXNrdG9wLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2ludGVsLWdmeAo= From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751743AbeACHOz convert rfc822-to-8bit (ORCPT + 1 other); Wed, 3 Jan 2018 02:14:55 -0500 Received: from mga02.intel.com ([134.134.136.20]:3562 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751205AbeACHOx (ORCPT ); Wed, 3 Jan 2018 02:14:53 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.45,500,1508828400"; d="scan'208";a="16402641" From: Jani Nikula To: Chris Wilson , Rodrigo Vivi , Stefan =?utf-8?Q?Br=C3=BCns?= Cc: David Airlie , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: Re: [Intel-gfx] [PATCH v2] drm/i915: Try EDID bitbanging on HDMI after failed read In-Reply-To: <151492106622.21495.250228197580562391@mail.alporthouse.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20180102191218.53beopvnxsg2etmg@intel.com> <151492106622.21495.250228197580562391@mail.alporthouse.com> Date: Wed, 03 Jan 2018 09:14:47 +0200 Message-ID: <87vagj2z2w.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Tue, 02 Jan 2018, Chris Wilson wrote: > Quoting Rodrigo Vivi (2018-01-02 19:12:18) >> On Sun, Dec 31, 2017 at 10:34:54PM +0000, Stefan Brüns wrote: >> > + edid = drm_get_edid(connector, i2c); >> > + >> > + if (!edid && !intel_gmbus_is_forced_bit(i2c)) { >> > + DRM_DEBUG_KMS("HDMI GMBUS EDID read failed, retry using GPIO bit-banging\n"); >> > + intel_gmbus_force_bit(i2c, true); >> > + edid = drm_get_edid(connector, i2c); >> > + intel_gmbus_force_bit(i2c, false); >> > + } >> >> Approach seems fine for this case. >> I just wonder what would be the risks of forcing this bit and edid read when nothing is present on the other end? > > Should be no more risky than using GMBUS as the bit-banging is the > underlying HW protocol; it should just be adding an extra delay to > the disconnected probe. Offset against the chance that it fixes > detection of borderline devices. > > I would say that given the explanation above, the question is why not > apply it universally? (Bonus points for including the explanation as > comments.) I'm wondering, is gmbus too fast for the adapters, does gmbus generally have different timing for the ack/nak as described in the commit message than bit banging, or are the adapters just plain buggy? Do we have any control over gmbus timings (don't have the time to peruse the bpsec just now)? BR, Jani. > -Chris > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Jani Nikula, Intel Open Source Technology Center