From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 75A513209; Wed, 7 May 2025 06:05:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746597939; cv=none; b=pC8hmZo1kE22gs9lcDn8dHxSthmKYPNTczEHAakJVtU7JsjZx20oPdU1KOJd4uAa3y2/tjOwaoKlNtmd9KgYZMGXNuF3W8LX41S7Y5qO7ep+AN1buzxROazPDnmWCmBoGFgyXU6mEqP2vtTIizrgtDmQSymAICMBX7IMxArNOOI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746597939; c=relaxed/simple; bh=MxaitG3CeVKWMYfeMyrLf5dhe0p3NY2WKRP6bXurY4A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=J/Cjk0PkbzCpFolxhI+/ucO1Tnz6uuo8t88jUjJCuaTqYNysfYc3x1cGWaFWnX4yS6srNK2pvaujPYBXlIRUP9aGxt/PXwZDqau8Y1wfc3vUfawqRXRI/xl13Wu8azj6lQWYO75PlNcIyoufd9f5gV8KndvmuXCmahqWsbWdDxA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Xydg6riZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Xydg6riZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 927D5C4CEE7; Wed, 7 May 2025 06:05:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746597938; bh=MxaitG3CeVKWMYfeMyrLf5dhe0p3NY2WKRP6bXurY4A=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Xydg6riZZiopOfjrEFs9cFM5vjxkDdxaMx26gHeyNlsv+htBqzNyK7TVu8UV47g/W FyiB8SBP7pt7G4J8OkZgHtZmi96TDgsuoZAouple+rlD9GrEqkguTWHMr2DbhbSxX4 9gAxC2ZFcu4W783A17jlYjR/ObGNRnbN0QZ0S1BN3qRHsZa3YxFFBTiOwHlYxoGPyr t41ThI81r1N88XNZ6lUB1DJp6DQxNkv6LxFKj77YtSa7H8gWLPG+ANoy04+v4wukif C1jtgshJvfUr5cTyxig5zIyf/uRaD40LVREPv1kz+Wm8qi+E6BnD7uZuOXzSnAcPlv DzZXeYATjqonA== Message-ID: Date: Wed, 7 May 2025 08:05:35 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] tty: serial: 8250_omap: fix tx with dma To: Mans Rullgard Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux-omap@vger.kernel.org, stable@vger.kernel.org References: <20250506150748.3162-1-mans@mansr.com> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 06. 05. 25, 17:07, Mans Rullgard wrote: > Commit 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") > introduced an error in the TX DMA handling for 8250_omap. > > When the OMAP_DMA_TX_KICK flag is set, one byte is pulled from the > kfifo and emitted directly in order to start the DMA. This is done > without updating DMA tx_size which leads to uart_xmit_advance() called > in the DMA complete callback advancing the kfifo by one too much. > > In practice, transmitting N bytes has been seen to result in the last > N-1 bytes being sent repeatedly. > > This change fixes the problem by moving all of the dma setup after > the OMAP_DMA_TX_KICK handling and using kfifo_len() instead of the > dma size for the 4-byte cutoff check. This slightly changes the > behaviour at buffer wraparound, but it still transmits the correct > bytes somehow. At the point kfifo_dma_out_prepare_mapped is called, > at least one byte is guaranteed to be in the fifo, so checking the > return value is not necessary. > > Fixes: 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") > Cc: stable@vger.kernel.org > Signed-off-by: Mans Rullgard > --- > v2: split patch in two > --- > drivers/tty/serial/8250/8250_omap.c | 24 +++++++++--------------- > 1 file changed, 9 insertions(+), 15 deletions(-) > > diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c > index f1aee915bc02..180466e09605 100644 > --- a/drivers/tty/serial/8250/8250_omap.c > +++ b/drivers/tty/serial/8250/8250_omap.c > @@ -1173,16 +1173,6 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) > return 0; > } > > - sg_init_table(&sg, 1); > - ret = kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1, > - UART_XMIT_SIZE, dma->tx_addr); > - if (ret != 1) { > - serial8250_clear_THRI(p); > - return 0; > - } > - > - dma->tx_size = sg_dma_len(&sg); > - > if (priv->habit & OMAP_DMA_TX_KICK) { > unsigned char c; > u8 tx_lvl; ... > @@ -1216,11 +1206,12 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) > goto err; > } > skip_byte = c; > - /* now we need to recompute due to kfifo_get */ > - kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1, > - UART_XMIT_SIZE, dma->tx_addr); > } > > + sg_init_table(&sg, 1); > + kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1, > + UART_XMIT_SIZE, dma->tx_addr); This can fail (note the first call to this was checked). The latter (deliberately) not. > + > desc = dmaengine_prep_slave_sg(dma->txchan, &sg, 1, DMA_MEM_TO_DEV, > DMA_PREP_INTERRUPT | DMA_CTRL_ACK); > if (!desc) { ... > @@ -1248,8 +1240,10 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) > err: > dma->tx_err = 1; > out_skip: > - if (skip_byte >= 0) > + if (skip_byte >= 0) { > serial_out(p, UART_TX, skip_byte); > + p->port.icount.tx++; This is still unrelated. thanks, -- js suse labs