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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26BC7C432BE for ; Wed, 18 Aug 2021 16:17:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0898F60231 for ; Wed, 18 Aug 2021 16:17:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231373AbhHRQSb (ORCPT ); Wed, 18 Aug 2021 12:18:31 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:41390 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231285AbhHRQSa (ORCPT ); Wed, 18 Aug 2021 12:18:30 -0400 Date: Wed, 18 Aug 2021 18:17:52 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1629303473; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=COIZjFE+QpiqW1vgmef7bfSA5uIv7ItVkGPh67WOnuI=; b=0tq0RyJndnU205fpXjnwy/AajvpF8L/7ellXA2SGrYReE5E8yIxdLYsh5gmH1NJVrIjzaZ vYG6Zm2qcqLWlZ87qzTDl/Jy9CCjDIOiLhQcFt6VZWmpVhT9ABxwBI6VuH1nwQ9ibU92y0 AZuCvEdn9iO4rqQ3jQ9fECg3G2N2ao4Dq325Z04vcZ2pRd6e/GO7oa19k5ALTRYzFavoAQ xrihDtMeby4S1F7Bc78N9DfuqV/pLKJuTCHmNmQPeMYF0xz8J+zl34XvbNraVuSWX4ZZJn LUHPFSE8lhN062LltrixFTXN2lcvC8CQIAPfbwGqqHMLcwe7Rv/28qBaLi6f6Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1629303473; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=COIZjFE+QpiqW1vgmef7bfSA5uIv7ItVkGPh67WOnuI=; b=UM8gwUAtzbvGGD8ByCKwJDdMCltoMKTzKUqQX2QMTEL9GuXRt1sKhCCeMeesnRHT6txoLO zmJ+s1Xd+W6U3EAA== From: Sebastian Andrzej Siewior To: Jeaho Hwang Cc: Peter Chen , Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, linux-rt-users@vger.kernel.org, team-linux@rtst.co.kr, mkbyeon@lselectric.co.kr, khchoib@lselectric.co.kr Subject: Re: [PATCH v2] usb: chipidea: local_irq_save/restore added for hw_ep_prime Message-ID: <20210818161752.vu6abfv3e6bfqz23@linutronix.de> References: <20210817095313.GA671484@ubuntu> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210817095313.GA671484@ubuntu> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-08-17 18:53:13 [+0900], Jeaho Hwang wrote: > hw_ep_prime sometimes fails if irq occurs while it rus on RT kernel. How/ why does it fail? Which IRQ occurs? Does it also occur without RT and with threadirqs enabled? > local_irq_save/restore is added inside the function to gurantee atomicity. > only effective for preempt_rt since hw_ep_prime is called inside top half > or spin_lock_irqsave. No effect is expected for standard linux. How is that helping? #1 udc_irq() -> isr_tr_complete_handler() -> isr_tr_complete_low -> _hardware_dequeue() -> reprime_dtd() -> hw_ep_prime() udc_irq() acquires ci->lock. #2 ep_queue -> _ep_queue() ->_hardware_enqueue() -> hw_ep_prime() ep_queue acquires hwep->lock. Which is actually ci->lock. So if I read this right then hw_ep_prime() may not be interrupted in the middle of its operation (but preempted) because each path is protected by the lock. isr_tr_complete_low() drops hwep->lock and acquires it again so it that phase another thread may acquire it. > Signed-off-by: Jeaho Hwang > > diff --git a/drivers/usb/chipidea/udc.c b/drivers/usb/chipidea/udc.c > index 8834ca613721..a624eddb3e22 100644 > --- a/drivers/usb/chipidea/udc.c > +++ b/drivers/usb/chipidea/udc.c > @@ -191,22 +191,31 @@ static int hw_ep_get_halt(struct ci_hdrc *ci, int num, int dir) > static int hw_ep_prime(struct ci_hdrc *ci, int num, int dir, int is_ctrl) > { > int n = hw_ep_bit(num, dir); > + unsigned long flags; > + int ret = 0; > > /* Synchronize before ep prime */ > wmb(); > > - if (is_ctrl && dir == RX && hw_read(ci, OP_ENDPTSETUPSTAT, BIT(num))) > + /* irq affects this routine so irq should be disabled on RT. > + * on standard kernel, irq is already disabled by callers. The important part is _how_ it is affected. If locking works then nothing should read/ write the HW register. If the lock is briefly dropped then another thread _may_ read/ write the registers but not within this function. If this function here is sensitive to timing (say the cpu_relax() loop gets interrupt for 1ms) then it has to be documented as such. > + */ > + local_irq_save(flags); > + if (is_ctrl && dir == RX && hw_read(ci, OP_ENDPTSETUPSTAT, BIT(num))) { > + local_irq_restore(flags); > return -EAGAIN; > + } > > hw_write(ci, OP_ENDPTPRIME, ~0, BIT(n)); > > while (hw_read(ci, OP_ENDPTPRIME, BIT(n))) > cpu_relax(); > if (is_ctrl && dir == RX && hw_read(ci, OP_ENDPTSETUPSTAT, BIT(num))) > - return -EAGAIN; > + ret = -EAGAIN; > > + local_irq_restore(flags); > /* status shoult be tested according with manual but it doesn't work */ > - return 0; > + return ret; > } > > /** Sebastian