From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?UTF-8?Q?Christian_K=c3=b6nig?= Subject: Re: [PATCH] drm/radeon: Retry DDC probing on DVI on failure if we got an HPD interrupt Date: Sat, 21 Nov 2015 16:22:28 +0100 Message-ID: <56508C34.1030909@amd.com> References: <1448034740-30193-1-git-send-email-cpaul@redhat.com> <56507E0F.7030009@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; Format="flowed" Content-Transfer-Encoding: base64 Return-path: Received: from na01-bl2-obe.outbound.protection.outlook.com (mail-bl2on0069.outbound.protection.outlook.com [65.55.169.69]) by gabe.freedesktop.org (Postfix) with ESMTPS id 7C5026E0A5 for ; Sat, 21 Nov 2015 07:22:54 -0800 (PST) In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Daniel Stone Cc: Linux Kernel Mailing List , dri-devel , Jerome Glisse , Benjamin Tissoires , Alex Deucher , cpaul@redhat.com List-Id: dri-devel@lists.freedesktop.org T24gMjEuMTEuMjAxNSAxNTo0OSwgRGFuaWVsIFN0b25lIHdyb3RlOgo+IEhpLAo+Cj4gT24gMjEg Tm92ZW1iZXIgMjAxNSBhdCAxNDoyMiwgQ2hyaXN0aWFuIEvDtm5pZyA8Y2hyaXN0aWFuLmtvZW5p Z0BhbWQuY29tPiB3cm90ZToKPj4gT24gMjAuMTEuMjAxNSAxNjo1MiwgY3BhdWxAcmVkaGF0LmNv bSB3cm90ZToKPj4+IFRoaXMgaXMgc29tZXdoYXQgcmFyZSBvbiBtb3N0IGNhcmRzIChkZXBlbmRp bmcgb24gd2hhdCBhbmdsZSB5b3UgcGx1Zwo+Pj4gdGhlIERWSSBjb25uZWN0b3IgaW4pLCBidXQg b24gc29tZSBjYXJkcyBpdCBoYXBwZW5zIGNvbnN0YW50bHkuIFRoZQo+Pj4gUmFkZW9uIFI1IG9u IHRoZSBtYWNoaW5lIHVzZWQgZm9yIHRlc3RpbmcgdGhpcyBwYXRjaCBmb3IgaW5zdGFuY2UsIHJ1 bnMKPj4+IGludG8gdGhpcyBpc3N1ZSBqdXN0IGFib3V0IGV2ZXJ5IHRpbWUgSSB0cnkgdG8gaG90 cGx1ZyBhIERWSSBtb25pdG9yIGFuZAo+Pj4gYXMgYSByZXN1bHQgaG90cGx1Z2dpbmcgYWxtb3N0 IG5ldmVyIHdvcmtzLgo+Pj4KPj4+IFJlc2NoZWR1bGluZyB0aGUgaG90cGx1ZyB3b3JrIGZvciBh IHNlY29uZCB3aGVuIHdlIHJ1biBpbnRvIGFuIEhQRAo+Pj4gc2lnbmFsIHdpdGggYSBmYWlsaW5n IEREQyBwcm9iZSB1c3VhbGx5IGdpdmVzIGVub3VnaCB0aW1lIGZvciB0aGUgcmVzdAo+Pj4gb2Yg dGhlIGNvbm5lY3RvcidzIHBpbnMgdG8gbWFrZSBjb250YWN0LCBhbmQgZml4ZXMgdGhpcyBpc3N1 ZS4KPj4+Cj4+PiBTaWduZWQtb2ZmLWJ5OiBTdGVwaGVuIENoYW5kbGVyIFBhdWwgPGNwYXVsQHJl ZGhhdC5jb20+Cj4+Cj4+IFllYWgsIHRoYXQncyBzb21ldGhpbmcgSSBhbHdheXMgd29uZGVyZWQg YSBhYm91dCBiaXQgYXMgd2VsbC4KPj4KPj4gRGVib3VuY2luZyBpcyBzb21ldGhpbmcgdmVyeSBj b21tb24gZG9uZSBpbiBlbGVjdHJvbmljcywgYnV0IGFzIGZhciBhcyBJCj4+IGtub3cgdGhlIEhQ RCBwaW5zIGRvbid0IG5lY2Vzc2FyeSBoYXZlIGFuIFJDIGNpcmN1aXQgc28gd2UgbWlnaHQgbmVl ZCB0bwo+PiBoYW5kbGUgdGhpcyBjYXNlIGluIHNvZnR3YXJlIGhlcmUuCj4+Cj4+IEEgZGVsYXkg b2Ygc29tZXRoaW5nIGJldHdlZW4gMTAtMzBtcyBiZXR3ZWVuIHRoZSBsYXN0IEhQRCBpbnRlcnJ1 cHQgYW5kCj4+IGZ1cnRoZXIgcHJvY2Vzc2luZyBvZiB0aGUgc2lnbmFsIGRvZXNuJ3Qgc291bmRz IGxpa2Ugc3VjaCBhIGJhZCBpZGVhLgo+Pgo+PiBSZXRyeWluZyBvbiB0aGUgb3RoZXIgaGFuZCBk b2Vzbid0IG5lY2Vzc2FyaWx5IGltcHJvdmUgdGhlIHNpdHVhdGlvbiBjYXVzZQo+PiB0aGUgZGVs YXkgaW50cm9kdWNlZCBieSB0aGlzIG1pZ2h0IG5vdCBiZSBlbm91Z2guCj4+Cj4+IFNvIEkgd291 bGQgcmF0aGVyIHZvdGUgZm9yIGEgZml4ZWQgZGVsYXkgYmV0d2VlbiBhbiBIUEQgaW50ZXJydXB0 IGFuZAo+PiBhY3R1YWxseSBzdGFydGluZyB0byBwcm9jZXNzIGFueXRoaW5nLgo+IFllcy1pc2gu IERlYm91bmNpbmcgaXMgdXNlZnVsLCBhbmQgaWdub3JpbmcgYnVnZ3kgZGV2aWNlcyAoZS5nLiB0 aG9zZQo+IG9uIG1hcmdpbmFsIHBvd2VyKSB3aGljaCBzZW5kIHlvdSBIUEQgc3Rvcm1zIGFzIHdl bGwuIEJ1dCBEUCByZWxpZXMgb24KPiAnc2hvcnQgSFBEJyBwdWxzZXMgd2hpY2ggY2FuIGJlIGFz IGJyaWVmIGFzIDJtcy4gU28gYXR0ZW1wdGluZyB0bwo+IHRvdGFsbHkgZGVib3VuY2UgYWxsIEhQ RCB3b24ndCB3b3JrLgpXZWxsIHRoZSBkaXNjdXNzaW9uIHNvIGZhciB3YXMgYWJvdXQgSFBEIG9u IERWSSBvbmx5LgoKSSdtIG5vdCBzbyBkZWVwIGludG8gRFAsIGJ1dCB3aHkgc2hvdWxkIGl0IHVz ZXMgSFBEIHB1bHNlcyBvZiBsZXNzIHRoYW4gMm1zPwoKUmVnYXJkcywKQ2hyaXN0aWFuLgoKPgo+ IENoZWVycywKPiBEYW5pZWwKCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fCmRyaS1kZXZlbCBtYWlsaW5nIGxpc3QKZHJpLWRldmVsQGxpc3RzLmZyZWVkZXNr dG9wLm9yZwpodHRwOi8vbGlzdHMuZnJlZWRlc2t0b3Aub3JnL21haWxtYW4vbGlzdGluZm8vZHJp LWRldmVsCg== From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761311AbbKUPW4 (ORCPT ); Sat, 21 Nov 2015 10:22:56 -0500 Received: from mail-bl2on0099.outbound.protection.outlook.com ([65.55.169.99]:19328 "EHLO na01-bl2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753074AbbKUPWy (ORCPT ); Sat, 21 Nov 2015 10:22:54 -0500 X-Greylist: delayed 3623 seconds by postgrey-1.27 at vger.kernel.org; Sat, 21 Nov 2015 10:22:53 EST Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=Christian.Koenig@amd.com; Subject: Re: [PATCH] drm/radeon: Retry DDC probing on DVI on failure if we got an HPD interrupt To: Daniel Stone References: <1448034740-30193-1-git-send-email-cpaul@redhat.com> <56507E0F.7030009@amd.com> CC: , Alex Deucher , David Airlie , dri-devel , "Linux Kernel Mailing List" , Jerome Glisse , Benjamin Tissoires From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <56508C34.1030909@amd.com> Date: Sat, 21 Nov 2015 16:22:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; 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The >>> Radeon R5 on the machine used for testing this patch for instance, runs >>> into this issue just about every time I try to hotplug a DVI monitor and >>> as a result hotplugging almost never works. >>> >>> Rescheduling the hotplug work for a second when we run into an HPD >>> signal with a failing DDC probe usually gives enough time for the rest >>> of the connector's pins to make contact, and fixes this issue. >>> >>> Signed-off-by: Stephen Chandler Paul >> >> Yeah, that's something I always wondered a about bit as well. >> >> Debouncing is something very common done in electronics, but as far as I >> know the HPD pins don't necessary have an RC circuit so we might need to >> handle this case in software here. >> >> A delay of something between 10-30ms between the last HPD interrupt and >> further processing of the signal doesn't sounds like such a bad idea. >> >> Retrying on the other hand doesn't necessarily improve the situation cause >> the delay introduced by this might not be enough. >> >> So I would rather vote for a fixed delay between an HPD interrupt and >> actually starting to process anything. > Yes-ish. Debouncing is useful, and ignoring buggy devices (e.g. those > on marginal power) which send you HPD storms as well. But DP relies on > 'short HPD' pulses which can be as brief as 2ms. So attempting to > totally debounce all HPD won't work. Well the discussion so far was about HPD on DVI only. I'm not so deep into DP, but why should it uses HPD pulses of less than 2ms? Regards, Christian. > > Cheers, > Daniel