From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A0900C433EF for ; Mon, 11 Apr 2022 09:57:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344912AbiDKJ7L (ORCPT ); Mon, 11 Apr 2022 05:59:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344928AbiDKJ7G (ORCPT ); Mon, 11 Apr 2022 05:59:06 -0400 Received: from muru.com (muru.com [72.249.23.125]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id B5DD041638; Mon, 11 Apr 2022 02:56:46 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by muru.com (Postfix) with ESMTPS id 625B081D0; Mon, 11 Apr 2022 09:54:15 +0000 (UTC) Date: Mon, 11 Apr 2022 12:56:44 +0300 From: Tony Lindgren To: Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= Cc: Greg Kroah-Hartman , Jiri Slaby , Johan Hovold , linux-serial@vger.kernel.org, kernel@pengutronix.de, Steffen Trumtrar , linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org, regressions@lists.linux.dev Subject: Re: [PATCH] serial: 8250: Return early in .start_tx() if there are no chars to send Message-ID: References: <20220217211839.443039-1-u.kleine-koenig@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-omap@vger.kernel.org * Tony Lindgren [220407 13:25]: > Hi, > > * Uwe Kleine-König [700101 02:00]: > > From: Steffen Trumtrar > > > > Don't start the whole chain for TX if there is no data to send. This is > > mostly relevant for rs485 mode as there might be rts-before-send and > > rts-after-send delays involved. > > > > Signed-off-by: Steffen Trumtrar > > Signed-off-by: Uwe Kleine-König > > --- > > Hello, > > > > a few other drivers have such an early exit already (imx, stm32-usart). > > I wonder if it applies to all UART drivers that there is nothing to do > > in .start_tx() if the circ buffer is empty and there is no x_char to > > send. In this case it would be more sensible to ensure in serial_core > > that .start_tx() is only ever called if there is something to do. > > This patch seems to cause a runtime PM regression in v5.18-rc1 where > 8250 is never idled for omaps. > > Looks like the return added here is not paired with put for the > serial8250_rpm_get_tx() call above? FYI I just posted two fixes for these early return cases: https://lore.kernel.org/linux-serial/20220411094805.45696-1-tony@atomide.com/T/#t Regards, Tony From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5D0DAC433EF for ; Mon, 11 Apr 2022 10:28:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; 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charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org KiBUb255IExpbmRncmVuIDx0b255QGF0b21pZGUuY29tPiBbMjIwNDA3IDEzOjI1XToKPiBIaSwK PiAKPiAqIFV3ZSBLbGVpbmUtS8O2bmlnIDx1LmtsZWluZS1rb2VuaWdAcGVuZ3V0cm9uaXguZGU+ IFs3MDAxMDEgMDI6MDBdOgo+ID4gRnJvbTogU3RlZmZlbiBUcnVtdHJhciA8cy50cnVtdHJhckBw ZW5ndXRyb25peC5kZT4KPiA+IAo+ID4gRG9uJ3Qgc3RhcnQgdGhlIHdob2xlIGNoYWluIGZvciBU WCBpZiB0aGVyZSBpcyBubyBkYXRhIHRvIHNlbmQuIFRoaXMgaXMKPiA+IG1vc3RseSByZWxldmFu dCBmb3IgcnM0ODUgbW9kZSBhcyB0aGVyZSBtaWdodCBiZSBydHMtYmVmb3JlLXNlbmQgYW5kCj4g PiBydHMtYWZ0ZXItc2VuZCBkZWxheXMgaW52b2x2ZWQuCj4gPiAKPiA+IFNpZ25lZC1vZmYtYnk6 IFN0ZWZmZW4gVHJ1bXRyYXIgPHMudHJ1bXRyYXJAcGVuZ3V0cm9uaXguZGU+Cj4gPiBTaWduZWQt b2ZmLWJ5OiBVd2UgS2xlaW5lLUvDtm5pZyA8dS5rbGVpbmUta29lbmlnQHBlbmd1dHJvbml4LmRl Pgo+ID4gLS0tCj4gPiBIZWxsbywKPiA+IAo+ID4gYSBmZXcgb3RoZXIgZHJpdmVycyBoYXZlIHN1 Y2ggYW4gZWFybHkgZXhpdCBhbHJlYWR5IChpbXgsIHN0bTMyLXVzYXJ0KS4KPiA+IEkgd29uZGVy IGlmIGl0IGFwcGxpZXMgdG8gYWxsIFVBUlQgZHJpdmVycyB0aGF0IHRoZXJlIGlzIG5vdGhpbmcg dG8gZG8KPiA+IGluIC5zdGFydF90eCgpIGlmIHRoZSBjaXJjIGJ1ZmZlciBpcyBlbXB0eSBhbmQg dGhlcmUgaXMgbm8geF9jaGFyIHRvCj4gPiBzZW5kLiBJbiB0aGlzIGNhc2UgaXQgd291bGQgYmUg bW9yZSBzZW5zaWJsZSB0byBlbnN1cmUgaW4gc2VyaWFsX2NvcmUKPiA+IHRoYXQgLnN0YXJ0X3R4 KCkgaXMgb25seSBldmVyIGNhbGxlZCBpZiB0aGVyZSBpcyBzb21ldGhpbmcgdG8gZG8uCj4gCj4g VGhpcyBwYXRjaCBzZWVtcyB0byBjYXVzZSBhIHJ1bnRpbWUgUE0gcmVncmVzc2lvbiBpbiB2NS4x OC1yYzEgd2hlcmUKPiA4MjUwIGlzIG5ldmVyIGlkbGVkIGZvciBvbWFwcy4KPiAKPiBMb29rcyBs aWtlIHRoZSByZXR1cm4gYWRkZWQgaGVyZSBpcyBub3QgcGFpcmVkIHdpdGggcHV0IGZvciB0aGUK PiBzZXJpYWw4MjUwX3JwbV9nZXRfdHgoKSBjYWxsIGFib3ZlPwoKRllJIEkganVzdCBwb3N0ZWQg dHdvIGZpeGVzIGZvciB0aGVzZSBlYXJseSByZXR1cm4gY2FzZXM6CgpodHRwczovL2xvcmUua2Vy bmVsLm9yZy9saW51eC1zZXJpYWwvMjAyMjA0MTEwOTQ4MDUuNDU2OTYtMS10b255QGF0b21pZGUu Y29tL1QvI3QKClJlZ2FyZHMsCgpUb255CgpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fX19fX19fXwpsaW51eC1hcm0ta2VybmVsIG1haWxpbmcgbGlzdApsaW51eC1hcm0t a2VybmVsQGxpc3RzLmluZnJhZGVhZC5vcmcKaHR0cDovL2xpc3RzLmluZnJhZGVhZC5vcmcvbWFp bG1hbi9saXN0aW5mby9saW51eC1hcm0ta2VybmVsCg==