From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754175AbeDMJrI (ORCPT ); Fri, 13 Apr 2018 05:47:08 -0400 Received: from mx07-00178001.pphosted.com ([62.209.51.94]:47607 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753254AbeDMJrG (ORCPT ); Fri, 13 Apr 2018 05:47:06 -0400 Subject: Re: [PATCH v2 1/2] dmaengine: stm32-mdma: align TLEN and buffer length on burst To: Robin Murphy , Vinod Koul , Maxime Coquelin , Alexandre Torgue , Dan Williams , "M'boumba Cedric Madianga" , , , References: <1523457879-9869-1-git-send-email-pierre-yves.mordret@st.com> <1523457879-9869-2-git-send-email-pierre-yves.mordret@st.com> <9a2a267c-2b0b-0d6a-c762-47e7d37f84ea@arm.com> From: Pierre Yves MORDRET Message-ID: <22bd0af7-9820-57c5-9215-8185839d7d27@st.com> Date: Fri, 13 Apr 2018 11:45:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <9a2a267c-2b0b-0d6a-c762-47e7d37f84ea@arm.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.75.127.50] X-ClientProxiedBy: SFHDAG4NODE3.st.com (10.75.127.12) To SFHDAG5NODE2.st.com (10.75.127.14) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-13_05:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Robin On 04/11/2018 05:14 PM, Robin Murphy wrote: > On 11/04/18 15:44, Pierre-Yves MORDRET wrote: >> Both buffer Transfer Length (TLEN if any) and transfer size have to be >> aligned on burst size (burst beats*bus width). >> >> Signed-off-by: Pierre-Yves MORDRET >> --- >> Version history: >> v1: >> * Initial >> v2: >> --- >> --- >> drivers/dma/stm32-mdma.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/dma/stm32-mdma.c b/drivers/dma/stm32-mdma.c >> index daa1602..fbcffa2 100644 >> --- a/drivers/dma/stm32-mdma.c >> +++ b/drivers/dma/stm32-mdma.c >> @@ -413,7 +413,7 @@ static u32 stm32_mdma_get_best_burst(u32 buf_len, u32 tlen, u32 max_burst, >> u32 best_burst = max_burst; >> u32 burst_len = best_burst * width; >> >> - while ((burst_len > 0) && (tlen % burst_len)) { >> + while ((burst_len > 0) && (((tlen | buf_len) & (burst_len - 1)) != 0)) { >> best_burst = best_burst >> 1; >> burst_len = best_burst * width; >> } > > FWIW, doesn't that whole loop come down to just: > > burst_len = min(ffs(tlen | buf_len), max_burst * width); No sure it ends as expected. or I miss something or don't understand this statement I tried with "relevant value" : i.e. best_burst = 32, Tlen=128(default) and buf_len = 64, width= 4. This statements gets me something wrong output => 7 instead of 16 * 4. I doubt :) > > ? > > Robin. >