From patchwork Thu Oct 29 00:16:56 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 7515311 Return-Path: X-Original-To: patchwork-linux-spi@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id B0F8BBEEA4 for ; Thu, 29 Oct 2015 00:17:11 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id B219A20943 for ; Thu, 29 Oct 2015 00:17:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9C965207CB for ; Thu, 29 Oct 2015 00:17:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932178AbbJ2ARI (ORCPT ); Wed, 28 Oct 2015 20:17:08 -0400 Received: from mezzanine.sirena.org.uk ([106.187.55.193]:39867 "EHLO mezzanine.sirena.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752051AbbJ2ARH (ORCPT ); Wed, 28 Oct 2015 20:17:07 -0400 Received: from [58.123.138.205] (helo=finisterre) by mezzanine.sirena.org.uk with esmtpsa (TLS1.2:RSA_AES_128_CBC_SHA1:128) (Exim 4.80) (envelope-from ) id 1Zratr-0006a4-D5; Thu, 29 Oct 2015 00:17:04 +0000 Received: from broonie by finisterre with local (Exim 4.86) (envelope-from ) id 1Zratk-0006be-IC; Thu, 29 Oct 2015 09:16:56 +0900 From: Mark Brown To: Edward Kigwana , Ricardo Ribalda Delgado , Mark Brown , stable@vger.kernel.org Cc: linux-spi@vger.kernel.org In-Reply-To: <1446045362-13650-1-git-send-email-ricardo.ribalda@gmail.com> Message-Id: Date: Thu, 29 Oct 2015 09:16:56 +0900 X-SA-Exim-Connect-IP: 58.123.138.205 X-SA-Exim-Mail-From: broonie@sirena.org.uk X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 Subject: Applied "spi/spi-xilinx: Fix race condition on last word read" to the spi tree X-SA-Exim-Version: 4.2.1 (built Mon, 26 Dec 2011 16:24:06 +0000) X-SA-Exim-Scanned: Yes (on mezzanine.sirena.org.uk) Sender: linux-spi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-spi@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The patch spi/spi-xilinx: Fix race condition on last word read has been applied to the spi tree at git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git All being well this means that it will be integrated into the linux-next tree (usually sometime in the next 24 hours) and sent to Linus during the next merge window (or sooner if it is a bug fix), however if problems are discovered then the patch may be dropped or reverted. You may get further e-mails resulting from automated or manual testing and review of the tree, please engage with people reporting problems and send followup patches addressing any issues that are reported if needed. If any updates are required or you are submitting further changes they should be sent as incremental updates against current git, existing patches will not be replaced. Please add any relevant lists and maintainers to the CCs when replying to this mail. Thanks, Mark From eca37c7c117460e2fbe4e32c991bff32a961f688 Mon Sep 17 00:00:00 2001 From: Ricardo Ribalda Delgado Date: Wed, 28 Oct 2015 16:16:02 +0100 Subject: [PATCH] spi/spi-xilinx: Fix race condition on last word read Some users have reported that in polled mode the driver fails randomly to read the last word of the transfer. The end condition used for the transmissions (in polled and irq mode) has been the TX_EMPTY flag. But Lars-Peter Clausen has identified a delay from the TX_EMPTY to the actual end of the data rx. I believe that this race condition has not been detected until now because of the latency added by the IRQ handler or the PCIe bridge. This bugs affects setups with low latency access to the spi core. This patch replaces the readout logic: For all the words, except the last one, the TX_EMPTY flag is used (and cached). If !TX_EMPY or is the last word. The status register is read and the RX_EMPTY flag is used. The performance is not affected: there is an extra read of the Status Register, but the readout can start as soon as there is a word in the buffer. Reported-by: Edward Kigwana Initial-fix-by: Lars-Peter Clausen Signed-off-by: Ricardo Ribalda Delgado Signed-off-by: Mark Brown Cc: stable@vger.kernel.org --- drivers/spi/spi-xilinx.c | 38 ++++++++++++++++++++++++-------------- 1 file changed, 24 insertions(+), 14 deletions(-) diff --git a/drivers/spi/spi-xilinx.c b/drivers/spi/spi-xilinx.c index a339c1e..3009121 100644 --- a/drivers/spi/spi-xilinx.c +++ b/drivers/spi/spi-xilinx.c @@ -270,6 +270,7 @@ static int xilinx_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t) while (remaining_words) { int n_words, tx_words, rx_words; + u32 sr; n_words = min(remaining_words, xspi->buffer_size); @@ -284,24 +285,33 @@ static int xilinx_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t) if (use_irq) { xspi->write_fn(cr, xspi->regs + XSPI_CR_OFFSET); wait_for_completion(&xspi->done); - } else - while (!(xspi->read_fn(xspi->regs + XSPI_SR_OFFSET) & - XSPI_SR_TX_EMPTY_MASK)) - ; - - /* A transmit has just completed. Process received data and - * check for more data to transmit. Always inhibit the - * transmitter while the Isr refills the transmit register/FIFO, - * or make sure it is stopped if we're done. - */ - if (use_irq) + /* A transmit has just completed. Process received data + * and check for more data to transmit. Always inhibit + * the transmitter while the Isr refills the transmit + * register/FIFO, or make sure it is stopped if we're + * done. + */ xspi->write_fn(cr | XSPI_CR_TRANS_INHIBIT, - xspi->regs + XSPI_CR_OFFSET); + xspi->regs + XSPI_CR_OFFSET); + sr = XSPI_SR_TX_EMPTY_MASK; + } else + sr = xspi->read_fn(xspi->regs + XSPI_SR_OFFSET); /* Read out all the data from the Rx FIFO */ rx_words = n_words; - while (rx_words--) - xilinx_spi_rx(xspi); + while (rx_words) { + if ((sr & XSPI_SR_TX_EMPTY_MASK) && (rx_words > 1)) { + xilinx_spi_rx(xspi); + rx_words--; + continue; + } + + sr = xspi->read_fn(xspi->regs + XSPI_SR_OFFSET); + if (!(sr & XSPI_SR_RX_EMPTY_MASK)) { + xilinx_spi_rx(xspi); + rx_words--; + } + } remaining_words -= n_words; }