From mboxrd@z Thu Jan 1 00:00:00 1970 From: jorge.ramirez-ortiz@linaro.org (Jorge Ramirez-Ortiz) Date: Thu, 26 Feb 2015 11:56:51 -0500 Subject: [PATCH v5] drivers/tty: amba: defer probing DMA availability until hw_init In-Reply-To: <1424969811-11197-1-git-send-email-jorge.ramirez-ortiz@linaro.org> References: <1424969811-11197-1-git-send-email-jorge.ramirez-ortiz@linaro.org> Message-ID: <1424969811-11197-2-git-send-email-jorge.ramirez-ortiz@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Fix a race condition that happens when device_initcall(pl011_dma_initicall) is executed before all the devices have been probed - this issue was observed on an hisi_6220 SoC (HiKey board from Linaro). The deferred driver probing framework relies on late_initcall to trigger deferred probes so it is just possible that, even with a valid DMA driver ready to be loaded, we fail to synchronize with it. The proposed implementation delays probing of the DMA until the uart device is opened. As hw_init is invoked on port startup and port resume - but the DMA probe is only required once - we avoid calling multiple times using a new field in uart_amba_port to track this scenario. This commit allows for subsequent attempts to associate an external DMA if the DMA driver was deferred at UART hw_init time. Signed-off-by: Jorge Ramirez-Ortiz --- drivers/tty/serial/amba-pl011.c | 95 +++++++++++++---------------------------- 1 file changed, 30 insertions(+), 65 deletions(-) diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 8d94c19..4ce98e9 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -164,6 +164,7 @@ struct uart_amba_port { bool using_rx_dma; struct pl011_dmarx_data dmarx; struct pl011_dmatx_data dmatx; + bool dma_probed; #endif }; @@ -261,10 +262,11 @@ static void pl011_sgbuf_free(struct dma_chan *chan, struct pl011_sgbuf *sg, } } -static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port *uap) +static void pl011_dma_probe(struct uart_amba_port *uap) { /* DMA is the sole user of the platform data right now */ - struct amba_pl011_data *plat = dev_get_platdata(uap->port.dev); + struct device *const uap_dev = uap->port.dev; + struct amba_pl011_data *plat = dev_get_platdata(uap_dev); struct dma_slave_config tx_conf = { .dst_addr = uap->port.mapbase + UART01x_DR, .dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE, @@ -275,12 +277,19 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port * struct dma_chan *chan; dma_cap_mask_t mask; - chan = dma_request_slave_channel(dev, "tx"); + uap->dma_probed = true; + + chan = dma_request_slave_channel_reason(uap_dev, "tx"); + if (IS_ERR(chan)) { + if (PTR_ERR(chan) == -EPROBE_DEFER) { + dev_info(uap_dev, "DMA driver not ready\n"); + uap->dma_probed = false; + return; + } - if (!chan) { /* We need platform data */ if (!plat || !plat->dma_filter) { - dev_info(uap->port.dev, "no DMA platform data\n"); + dev_info(uap_dev, "no DMA platform data\n"); return; } @@ -291,7 +300,7 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port * chan = dma_request_channel(mask, plat->dma_filter, plat->dma_tx_param); if (!chan) { - dev_err(uap->port.dev, "no TX DMA channel!\n"); + dev_err(uap_dev, "no TX DMA channel!\n"); return; } } @@ -299,17 +308,17 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port * dmaengine_slave_config(chan, &tx_conf); uap->dmatx.chan = chan; - dev_info(uap->port.dev, "DMA channel TX %s\n", + dev_info(uap_dev, "DMA channel TX %s\n", dma_chan_name(uap->dmatx.chan)); /* Optionally make use of an RX channel as well */ - chan = dma_request_slave_channel(dev, "rx"); + chan = dma_request_slave_channel(uap_dev, "rx"); if (!chan && plat->dma_rx_param) { chan = dma_request_channel(mask, plat->dma_filter, plat->dma_rx_param); if (!chan) { - dev_err(uap->port.dev, "no RX DMA channel!\n"); + dev_err(uap_dev, "no RX DMA channel!\n"); return; } } @@ -333,7 +342,7 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port * if (caps.residue_granularity == DMA_RESIDUE_GRANULARITY_DESCRIPTOR) { dma_release_channel(chan); - dev_info(uap->port.dev, + dev_info(uap_dev, "RX DMA disabled - no residue processing\n"); return; } @@ -362,75 +371,29 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port * plat->dma_rx_poll_timeout; else uap->dmarx.poll_timeout = 3000; - } else if (!plat && dev->of_node) { + } else if (!plat && uap_dev->of_node) { uap->dmarx.auto_poll_rate = of_property_read_bool( - dev->of_node, "auto-poll"); + uap_dev->of_node, "auto-poll"); if (uap->dmarx.auto_poll_rate) { u32 x; - if (0 == of_property_read_u32(dev->of_node, + if (0 == of_property_read_u32(uap_dev->of_node, "poll-rate-ms", &x)) uap->dmarx.poll_rate = x; else uap->dmarx.poll_rate = 100; - if (0 == of_property_read_u32(dev->of_node, + if (0 == of_property_read_u32(uap_dev->of_node, "poll-timeout-ms", &x)) uap->dmarx.poll_timeout = x; else uap->dmarx.poll_timeout = 3000; } } - dev_info(uap->port.dev, "DMA channel RX %s\n", + dev_info(uap_dev, "DMA channel RX %s\n", dma_chan_name(uap->dmarx.chan)); } } -#ifndef MODULE -/* - * Stack up the UARTs and let the above initcall be done at device - * initcall time, because the serial driver is called as an arch - * initcall, and at this time the DMA subsystem is not yet registered. - * At this point the driver will switch over to using DMA where desired. - */ -struct dma_uap { - struct list_head node; - struct uart_amba_port *uap; - struct device *dev; -}; - -static LIST_HEAD(pl011_dma_uarts); - -static int __init pl011_dma_initcall(void) -{ - struct list_head *node, *tmp; - - list_for_each_safe(node, tmp, &pl011_dma_uarts) { - struct dma_uap *dmau = list_entry(node, struct dma_uap, node); - pl011_dma_probe_initcall(dmau->dev, dmau->uap); - list_del(node); - kfree(dmau); - } - return 0; -} - -device_initcall(pl011_dma_initcall); - -static void pl011_dma_probe(struct device *dev, struct uart_amba_port *uap) -{ - struct dma_uap *dmau = kzalloc(sizeof(struct dma_uap), GFP_KERNEL); - if (dmau) { - dmau->uap = uap; - dmau->dev = dev; - list_add_tail(&dmau->node, &pl011_dma_uarts); - } -} -#else -static void pl011_dma_probe(struct device *dev, struct uart_amba_port *uap) -{ - pl011_dma_probe_initcall(dev, uap); -} -#endif - static void pl011_dma_remove(struct uart_amba_port *uap) { /* TODO: remove the initcall if it has not yet executed */ @@ -1142,7 +1105,7 @@ static inline bool pl011_dma_rx_running(struct uart_amba_port *uap) #else /* Blank functions if the DMA engine is not available */ -static inline void pl011_dma_probe(struct device *dev, struct uart_amba_port *uap) +static inline void pl011_dma_probe(struct uart_amba_port *uap) { } @@ -1548,6 +1511,9 @@ static int pl011_hwinit(struct uart_port *port) uap->im = readw(uap->port.membase + UART011_IMSC); writew(UART011_RTIM | UART011_RXIM, uap->port.membase + UART011_IMSC); + if (!uap->dma_probed) + pl011_dma_probe(uap); + if (dev_get_platdata(uap->port.dev)) { struct amba_pl011_data *plat; @@ -2218,7 +2184,6 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id) uap->port.ops = &amba_pl011_pops; uap->port.flags = UPF_BOOT_AUTOCONF; uap->port.line = i; - pl011_dma_probe(&dev->dev, uap); /* Ensure interrupts from this UART are masked and cleared */ writew(0, uap->port.membase + UART011_IMSC); @@ -2233,7 +2198,8 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id) if (!amba_reg.state) { ret = uart_register_driver(&amba_reg); if (ret < 0) { - pr_err("Failed to register AMBA-PL011 driver\n"); + dev_err(&dev->dev, + "Failed to register AMBA-PL011 driver\n"); return ret; } } @@ -2242,7 +2208,6 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id) if (ret) { amba_ports[i] = NULL; uart_unregister_driver(&amba_reg); - pl011_dma_remove(uap); } return ret; -- 1.9.1