From patchwork Tue Jan 5 19:42:52 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kamal Mostafa X-Patchwork-Id: 563334 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id 7B741140081; Wed, 6 Jan 2016 06:48:17 +1100 (AEDT) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1aGXaW-0003PV-CJ; Tue, 05 Jan 2016 19:48:12 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.76) (envelope-from ) id 1aGXZL-0002aJ-FT for kernel-team@lists.ubuntu.com; Tue, 05 Jan 2016 19:46:59 +0000 Received: from 1.general.kamal.us.vpn ([10.172.68.52] helo=fourier) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.76) (envelope-from ) id 1aGXZL-0005wA-2b; Tue, 05 Jan 2016 19:46:59 +0000 Received: from kamal by fourier with local (Exim 4.82) (envelope-from ) id 1aGXZI-0006pJ-Bb; Tue, 05 Jan 2016 11:46:56 -0800 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Subject: [PATCH 4.2.y-ckt 064/211] spi/spi-xilinx: Fix race condition on last word read Date: Tue, 5 Jan 2016 11:42:52 -0800 Message-Id: <1452023119-25647-65-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1452023119-25647-1-git-send-email-kamal@canonical.com> References: <1452023119-25647-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 4.2 Cc: Ricardo Ribalda Delgado , Kamal Mostafa , Mark Brown X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com 4.2.8-ckt1 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Ricardo Ribalda Delgado commit eca37c7c117460e2fbe4e32c991bff32a961f688 upstream. 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 Signed-off-by: Kamal Mostafa --- 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; }