[{"id":3680373,"web_url":"http://patchwork.ozlabs.org/comment/3680373/","msgid":"<98255b77-dcef-40c8-8851-91e723b82ea1@nvidia.com>","list_archive_url":null,"date":"2026-04-22T09:26:47","subject":"Re: [PATCH RESEND] dmaengine: tegra: Fix burst size calculation","submitter":{"id":66273,"url":"http://patchwork.ozlabs.org/api/people/66273/","name":"Jon Hunter","email":"jonathanh@nvidia.com"},"content":"On 22/04/2026 07:41, Kartik Rajput wrote:\n> Currently, the Tegra GPC DMA hardware requires the transfer length to\n> be a multiple of the max burst size configured for the channel. When a\n> client requests a transfer where the length is not evenly divisible by\n> the configured max burst size, the DMA hangs with partial burst at\n> the end.\n> \n> Fix this by reducing the burst size to the largest power-of-2 value\n> that evenly divides the transfer length. For example, a 40-byte\n> transfer with a 16-byte max burst will now use an 8-byte burst\n> (40 / 8 = 5 complete bursts) instead of causing a hang.\n> \n> This issue was observed with the PL011 UART driver where TX DMA\n> transfers of arbitrary lengths were stuck.\n> \n> Fixes: ee17028009d4 (\"dmaengine: tegra: Add tegra gpcdma driver\")\n> Cc: stable@vger.kernel.org\n> Signed-off-by: Kartik Rajput \n> Reviewed-by: Frank Li \n> ---\n> drivers/dma/tegra186-gpc-dma.c | 7 +++++++\n> 1 file changed, 7 insertions(+)\n> \n> diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-dma.c\n> index 5948fbf32c21..0aa3a02b2277 100644\n> --- a/drivers/dma/tegra186-gpc-dma.c\n> +++ b/drivers/dma/tegra186-gpc-dma.c\n> @@ -825,6 +825,13 @@ static unsigned int get_burst_size(struct tegra_dma_channel *tdc,\n> \t * len to calculate the optimum burst size\n> \t */\n> \tburst_byte = burst_size ? burst_size * slave_bw : len;\n> +\n> +\t/*\n> +\t * Find the largest burst size that evenly divides the transfer length.\n> +\t * The hardware requires the transfer length to be a multiple of the\n> +\t * burst size - partial bursts are not supported.\n> +\t */\n> +\tburst_byte = min(burst_byte, 1U << __ffs(len));\n> \tburst_mmio_width = burst_byte / 4;\n> \n> \tif (burst_mmio_width < TEGRA_GPCDMA_MMIOSEQ_BURST_MIN)\n\n\nReviewed-by: Jon Hunter \n\nThanks\nJon","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linux-tegra@vger.kernel.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=Nvidia.com header.i=@Nvidia.com header.a=rsa-sha256\n header.s=selector2 header.b=PtHtlA9X;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=172.232.135.74; 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