drivers/misc: Aspeed LPC snoop output using misc chardev

Provides the data bytes snooped over the LPC snoop bus to userspace
as a (blocking) misc character device.

Bytes output from the host using LPC I/O transactions to the snooped port
can be watched or retrieved from the character device using a simple
command like this:
~#  od -w1 -A n -t x1 /dev/aspeed-lpc-snoop0
 10
 de
 ad
 c0
 ff
 ee

Signed-off-by: Robert Lippert <rlippert@google.com>
Signed-off-by: Patrick Venture <venture@google.com>
Signed-off-by: Benjamin Fair <benjaminfair@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/misc/aspeed-lpc-snoop.c b/drivers/misc/aspeed-lpc-snoop.c
index cb78c98..2feb434 100644 (file)
--- a/drivers/misc/aspeed-lpc-snoop.c
+++ b/drivers/misc/aspeed-lpc-snoop.c
@@ -16,12 +16,15 @@
 
 #include <linux/bitops.h>
 #include <linux/interrupt.h>
+#include <linux/fs.h>
 #include <linux/kfifo.h>
 #include <linux/mfd/syscon.h>
+#include <linux/miscdevice.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
+#include <linux/poll.h>
 #include <linux/regmap.h>
 
 #define DEVICE_NAME    "aspeed-lpc-snoop"
@@ -59,20 +62,70 @@ struct aspeed_lpc_snoop_model_data {
        unsigned int has_hicrb_ensnp;
 };
 
+struct aspeed_lpc_snoop_channel {
+       struct kfifo            fifo;
+       wait_queue_head_t       wq;
+       struct miscdevice       miscdev;
+};
+
 struct aspeed_lpc_snoop {
        struct regmap           *regmap;
        int                     irq;
-       struct kfifo            snoop_fifo[NUM_SNOOP_CHANNELS];
+       struct aspeed_lpc_snoop_channel chan[NUM_SNOOP_CHANNELS];
+};
+
+static struct aspeed_lpc_snoop_channel *snoop_file_to_chan(struct file *file)
+{
+       return container_of(file->private_data,
+                           struct aspeed_lpc_snoop_channel,
+                           miscdev);
+}
+
+static ssize_t snoop_file_read(struct file *file, char __user *buffer,
+                               size_t count, loff_t *ppos)
+{
+       struct aspeed_lpc_snoop_channel *chan = snoop_file_to_chan(file);
+       unsigned int copied;
+       int ret = 0;
+
+       if (kfifo_is_empty(&chan->fifo)) {
+               if (file->f_flags & O_NONBLOCK)
+                       return -EAGAIN;
+               ret = wait_event_interruptible(chan->wq,
+                               !kfifo_is_empty(&chan->fifo));
+               if (ret == -ERESTARTSYS)
+                       return -EINTR;
+       }
+       ret = kfifo_to_user(&chan->fifo, buffer, count, &copied);
+
+       return ret ? ret : copied;
+}
+
+static unsigned int snoop_file_poll(struct file *file,
+                                   struct poll_table_struct *pt)
+{
+       struct aspeed_lpc_snoop_channel *chan = snoop_file_to_chan(file);
+
+       poll_wait(file, &chan->wq, pt);
+       return !kfifo_is_empty(&chan->fifo) ? POLLIN : 0;
+}
+
+static const struct file_operations snoop_fops = {
+       .owner  = THIS_MODULE,
+       .read   = snoop_file_read,
+       .poll   = snoop_file_poll,
+       .llseek = noop_llseek,
 };
 
 /* Save a byte to a FIFO and discard the oldest byte if FIFO is full */
-static void put_fifo_with_discard(struct kfifo *fifo, u8 val)
+static void put_fifo_with_discard(struct aspeed_lpc_snoop_channel *chan, u8 val)
 {
-       if (!kfifo_initialized(fifo))
+       if (!kfifo_initialized(&chan->fifo))
                return;
-       if (kfifo_is_full(fifo))
-               kfifo_skip(fifo);
-       kfifo_put(fifo, val);
+       if (kfifo_is_full(&chan->fifo))
+               kfifo_skip(&chan->fifo);
+       kfifo_put(&chan->fifo, val);
+       wake_up_interruptible(&chan->wq);
 }
 
 static irqreturn_t aspeed_lpc_snoop_irq(int irq, void *arg)
@@ -97,12 +150,12 @@ static irqreturn_t aspeed_lpc_snoop_irq(int irq, void *arg)
        if (reg & HICR6_STR_SNP0W) {
                u8 val = (data & SNPWDR_CH0_MASK) >> SNPWDR_CH0_SHIFT;
 
-               put_fifo_with_discard(&lpc_snoop->snoop_fifo[0], val);
+               put_fifo_with_discard(&lpc_snoop->chan[0], val);
        }
        if (reg & HICR6_STR_SNP1W) {
                u8 val = (data & SNPWDR_CH1_MASK) >> SNPWDR_CH1_SHIFT;
 
-               put_fifo_with_discard(&lpc_snoop->snoop_fifo[1], val);
+               put_fifo_with_discard(&lpc_snoop->chan[1], val);
        }
 
        return IRQ_HANDLED;
@@ -139,12 +192,22 @@ static int aspeed_lpc_enable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
        const struct aspeed_lpc_snoop_model_data *model_data =
                of_device_get_match_data(dev);
 
+       init_waitqueue_head(&lpc_snoop->chan[channel].wq);
        /* Create FIFO datastructure */
-       rc = kfifo_alloc(&lpc_snoop->snoop_fifo[channel],
+       rc = kfifo_alloc(&lpc_snoop->chan[channel].fifo,
                         SNOOP_FIFO_SIZE, GFP_KERNEL);
        if (rc)
                return rc;
 
+       lpc_snoop->chan[channel].miscdev.minor = MISC_DYNAMIC_MINOR;
+       lpc_snoop->chan[channel].miscdev.name =
+               devm_kasprintf(dev, GFP_KERNEL, "%s%d", DEVICE_NAME, channel);
+       lpc_snoop->chan[channel].miscdev.fops = &snoop_fops;
+       lpc_snoop->chan[channel].miscdev.parent = dev;
+       rc = misc_register(&lpc_snoop->chan[channel].miscdev);
+       if (rc)
+               return rc;
+
        /* Enable LPC snoop channel at requested port */
        switch (channel) {
        case 0:
@@ -191,7 +254,8 @@ static void aspeed_lpc_disable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
                return;
        }
 
-       kfifo_free(&lpc_snoop->snoop_fifo[channel]);
+       kfifo_free(&lpc_snoop->chan[channel].fifo);
+       misc_deregister(&lpc_snoop->chan[channel].miscdev);
 }
 
 static int aspeed_lpc_snoop_probe(struct platform_device *pdev)