[PATCH v4] drivers/tty: amba: defer probing DMA availability until hw_init
Jorge Ramirez-Ortiz
jorge.ramirez-ortiz at linaro.org
Thu Feb 26 08:50:20 PST 2015
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>
---
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..1404b80 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
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