[PATCH] drivers/tty: amba-pl011: defer driver probing if external dma is not ready.
Rob Herring
robh at kernel.org
Mon Feb 23 12:58:12 PST 2015
+spear maintainers
On Mon, Feb 23, 2015 at 2:16 PM, Jorge Ramirez-Ortiz
<jorge.ramirez-ortiz at linaro.org> wrote:
> This patch addresses 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 proposed implementation uses deferred driver probing to wait for the DMA
> controller to be registered.
This is going to break implementations using platform data rather than
DT for the DMA channel resolving. The only user is spear3xx. Ideally,
we should fix spear3xx to use DT for the DMA channels. That would
mainly require making the pl08x driver DT enabled and dts updates.
To fix this in the pl011 driver, you are going to need to split up the
DT and platform data paths keeping the list used for the platform
data. The platform data is only used for DMA and is mutually exclusive
with DT, so in probe you can do something like this:
if (pdata)
pdata_dma_probe();
else if (of_dma_probe() == -EPROBE_DEFER)
return -EPROBE_DEFER;
Rob
>
> Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz at linaro.org>
> ---
> drivers/tty/serial/amba-pl011.c | 70 +++++++++++------------------------------
> 1 file changed, 18 insertions(+), 52 deletions(-)
>
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index 8d94c19..40219e5 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -29,6 +29,7 @@
> * and hooked into this driver.
> */
>
> +#define pr_fmt(fmt) "amba-pl011: "fmt
>
> #if defined(CONFIG_SERIAL_AMBA_PL011_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
> #define SUPPORT_SYSRQ
> @@ -261,7 +262,7 @@ 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 int pl011_dma_probe(struct device *dev, 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);
> @@ -275,13 +276,17 @@ 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");
> + chan = dma_request_slave_channel_reason(dev, "tx");
> + if (IS_ERR(chan)) {
> +
> + /* the dma driver has not been initialized yet */
> + if (PTR_ERR(chan) == -EPROBE_DEFER)
> + return -EPROBE_DEFER;
>
> - if (!chan) {
> /* We need platform data */
> if (!plat || !plat->dma_filter) {
> dev_info(uap->port.dev, "no DMA platform data\n");
> - return;
> + return 0;
> }
>
> /* Try to acquire a generic DMA engine slave TX channel */
> @@ -292,7 +297,7 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port *
> plat->dma_tx_param);
> if (!chan) {
> dev_err(uap->port.dev, "no TX DMA channel!\n");
> - return;
> + return 0;
> }
> }
>
> @@ -310,7 +315,7 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port *
>
> if (!chan) {
> dev_err(uap->port.dev, "no RX DMA channel!\n");
> - return;
> + return 0;
> }
> }
>
> @@ -383,54 +388,10 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port *
> dev_info(uap->port.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 */
> @@ -1142,8 +1103,9 @@ 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 int pl011_dma_probe(struct device *dev, struct uart_amba_port *uap)
> {
> + return 0;
> }
>
> static inline void pl011_dma_remove(struct uart_amba_port *uap)
> @@ -2218,7 +2180,11 @@ 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);
> + ret = pl011_dma_probe(&dev->dev, uap);
> + if (ret) {
> + devm_kfree(&dev->dev, uap);
> + return ret;
> + }
>
> /* Ensure interrupts from this UART are masked and cleared */
> writew(0, uap->port.membase + UART011_IMSC);
> --
> 1.9.1
>
More information about the linux-arm-kernel
mailing list