[PATCH v5] drivers/tty: amba: defer probing DMA availability until hw_init
Rob Herring
robh at kernel.org
Tue Mar 3 08:13:21 PST 2015
On Thu, Feb 26, 2015 at 10:56 AM, Jorge Ramirez-Ortiz
<jorge.ramirez-ortiz at linaro.org> 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 <jorge.ramirez-ortiz at linaro.org>
You need to send this to Greg KH and linux-serial if you want it applied.
[...]
> @@ -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 <robh at kernel.org>
> + 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
>
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