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Thu, 22 Oct 2026 16:27:01 +0000 Date: Thu, 22 Oct 2026 11:26:51 -0500 From: Frank Li To: James Hilliard Cc: Vinod Koul , Frank Li , Chen-Yu Tsai , Jernej Skrabec , Samuel Holland , dmaengine@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] dmaengine: sun6i: bound burst selection before shifting Message-ID: References: <20261021-submit-sun6i-dma-burst-limit-v1-v1-1-41a7a476ef66@gmail.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261021-submit-sun6i-dma-burst-limit-v1-v1-1-41a7a476ef66@gmail.com> X-ClientProxiedBy: PH8P220CA0032.NAMP220.PROD.OUTLOOK.COM (2603:10b6:510:348::10) To MI3PR04MB12438.eurprd04.prod.outlook.com (2603:10a6:290:76::14) X-Archived-By: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MI3PR04MB12438:EE_|BESPR04MB068037:EE_ X-MS-Office365-Filtering-Correlation-Id: 4e306486-ab42-4a37-83c9-08df30594cd3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|19092799006|376014|1800799024|23010399003|7416014|18002099003|22082099003|11063799006|261009223027099003|261021121427099003|10067099003|56012099006; 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DesignWare UARTs request a maximum burst of > one quarter of their FIFO size, so a 256-byte FIFO supplies 64. Shifting > an unsigned long by 64 is undefined even on a 64-bit CPU. The fallback > loop can repeat the same invalid shift. > > Limit the search to the highest burst represented in the controller's > nonzero capability mask before either shift. Larger client limits still > select the largest supported burst, while smaller limits retain the > existing power-of-two selection and the zero/default case is unchanged. > > Fixes: 7178c3586ab4 ("dmaengine: sun6i: Choose appropriate burst length under maxburst") > Signed-off-by: James Hilliard > --- Reviewed-by: Frank Li > drivers/dma/sun6i-dma.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c > index 7704b016aed8..a8b12262b3c3 100644 > --- a/drivers/dma/sun6i-dma.c > +++ b/drivers/dma/sun6i-dma.c > @@ -590,6 +590,9 @@ static u32 find_burst_size(const u32 burst_lengths, u32 maxburst) > if (!maxburst) > return 1; > > + /* maxburst is a transfer limit, not necessarily a valid bit index. */ > + maxburst = min_t(u32, maxburst, fls(burst_lengths) - 1); > + > if (BIT(maxburst) & burst_lengths) > return maxburst; > > > --- > base-commit: 93f51579e7df248780214094418f205253383cc5 > change-id: 20261021-submit-sun6i-dma-burst-limit-v1-47e32971471e > > Best regards, > -- > James Hilliard >