From mboxrd@z Thu Jan 1 00:00:00 1970 From: jorge.ramirez-ortiz@linaro.org (Jorge Ramirez-Ortiz) Date: Tue, 03 Mar 2015 11:06:32 -0500 Subject: [PATCH v5] drivers/tty: amba: defer probing DMA availability until hw_init In-Reply-To: <1424969811-11197-2-git-send-email-jorge.ramirez-ortiz@linaro.org> 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: <54F5DC08.1040807@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 02/26/2015 11:56 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 > --- > 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; just following up on this fix (the current driver is broken on my tests). Is it acceptable at this point?