From mboxrd@z Thu Jan 1 00:00:00 1970 From: jorge.ramirez-ortiz@linaro.org (Jorge Ramirez-Ortiz) Date: Wed, 04 Mar 2015 16:33:51 -0500 Subject: [PATCH v5] drivers/tty: amba: defer probing DMA availability until hw_init In-Reply-To: References: <1424969811-11197-1-git-send-email-jorge.ramirez-ortiz@linaro.org> <1424969811-11197-2-git-send-email-jorge.ramirez-ortiz@linaro.org> Message-ID: <54F77A3F.5000300@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 03/03/2015 11:13 AM, Rob Herring wrote: > On Thu, Feb 26, 2015 at 10:56 AM, Jorge Ramirez-Ortiz > wrote: >> 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 > You need to send this to Greg KH and linux-serial if you want it applied. > > [...] ok. > >> @@ -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; > Call this "dev" so you don't have all the needless renaming. > > With that change: > > Reviewed-by: Rob Herring OK. while I am at it, you initially suggested to do the probe in pl011_dma_startup. Instead I probed from pl011_hwinit since it matched the original behaviour of also probing the DMA when CONFIG_CONSOLE_POLL was enabled. However, since the CONFIG_CONSOLE_POLL implementation for the amba-pl011 doesn't use the DMA it actually doesn't help to keep it in pl011_hwinit. is it ok with you if I move this to pl011_dma_startup as you initially suggested? > >> + 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; >> }amba-pl011.c >> >> @@ -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 >>