From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757379AbdJKLvt (ORCPT ); Wed, 11 Oct 2017 07:51:49 -0400 Received: from mail.free-electrons.com ([62.4.15.54]:56753 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756900AbdJKLvr (ORCPT ); Wed, 11 Oct 2017 07:51:47 -0400 Date: Wed, 11 Oct 2017 13:51:45 +0200 From: Boris Brezillon To: Eric Anholt Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] drm/vc4: Fix sleeps during the IRQ handler for DSI transactions. Message-ID: <20171011135145.6701b38a@bbrezillon> In-Reply-To: <20170817210455.17885-1-eric@anholt.net> References: <20170817210455.17885-1-eric@anholt.net> X-Mailer: Claws Mail 3.14.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 17 Aug 2017 14:04:55 -0700 Eric Anholt wrote: > VC4's DSI1 has a bug where the AXI connection is broken for 32-bit > writes from the CPU, so we use the DMA engine to DMA 32-bit values > into registers instead. That sleeps, so we can't do it from the top > half. > > As a solution (suggested by Arnd), we can mask the IRQ in the irqchip > in the top half, and re-enable it from an irqthread. > > Signed-off-by: Eric Anholt > --- > drivers/gpu/drm/vc4/vc4_dsi.c | 39 +++++++++++++++++++++++++++++++++++++-- > 1 file changed, 37 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c > index ec1d646b3151..9556236b67d0 100644 > --- a/drivers/gpu/drm/vc4/vc4_dsi.c > +++ b/drivers/gpu/drm/vc4/vc4_dsi.c > @@ -516,6 +516,8 @@ struct vc4_dsi { > /* Whether we're on bcm2835's DSI0 or DSI1. */ > int port; > > + int irq; > + > /* DSI channel for the panel we're connected to. */ > u32 channel; > u32 lanes; > @@ -1360,6 +1362,28 @@ static void dsi_handle_error(struct vc4_dsi *dsi, > *ret = IRQ_HANDLED; > } > > +/* Initial handler for port 1 where we need the reg_dma workaround. > + * The register DMA writes sleep, so we can't do it in the top half. > + * Instead we just disable the interrupt in the only way we have > + * available (mask it in the irqchip), and continue on to the threaded > + * handler. > + */ > +static irqreturn_t vc4_dsi_irq_defer_to_thread_handler(int irq, void *data) > +{ > + struct vc4_dsi *dsi = data; > + u32 stat = DSI_PORT_READ(INT_STAT); > + > + if (!stat) > + return IRQ_NONE; > + > + disable_irq_nosync(dsi->irq); Are you sure you need to explicitly disable the IRQ here? Did you try with an IRQF_ONESHOT flag when registering your irq handler (this should do exactly what you're doing here: mask the interrupt until the threaded handler returns IRQ_DONE or IRQ_NONE [1])? [1]http://elixir.free-electrons.com/linux/v4.3.2/source/include/linux/interrupt.h#L50 > + > + return IRQ_WAKE_THREAD; > +} > + > +/* Normal IRQ handler for port 0, or the threaded IRQ handler for port > + * 1 where we need the reg_dma workaround. > + */ > static irqreturn_t vc4_dsi_irq_handler(int irq, void *data) > { > struct vc4_dsi *dsi = data; > @@ -1368,6 +1392,9 @@ static irqreturn_t vc4_dsi_irq_handler(int irq, void *data) > > DSI_PORT_WRITE(INT_STAT, stat); > > + if (dsi->reg_dma_mem) > + enable_irq(dsi->irq); > + > dsi_handle_error(dsi, &ret, stat, > DSI1_INT_ERR_SYNC_ESC, "LPDT sync"); > dsi_handle_error(dsi, &ret, stat, > @@ -1539,8 +1566,16 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data) > /* Clear any existing interrupt state. */ > DSI_PORT_WRITE(INT_STAT, DSI_PORT_READ(INT_STAT)); > > - ret = devm_request_irq(dev, platform_get_irq(pdev, 0), > - vc4_dsi_irq_handler, 0, "vc4 dsi", dsi); > + dsi->irq = platform_get_irq(pdev, 0); > + if (dsi->reg_dma_mem) { > + ret = devm_request_threaded_irq(dev, dsi->irq, > + vc4_dsi_irq_defer_to_thread_handler, > + vc4_dsi_irq_handler, 0, > + "vc4 dsi", dsi); > + } else { > + ret = devm_request_irq(dev, dsi->irq, > + vc4_dsi_irq_handler, 0, "vc4 dsi", dsi); > + } > if (ret) { > if (ret != -EPROBE_DEFER) > dev_err(dev, "Failed to get interrupt: %d\n", ret);