Re: [PATCH v3 07/12] soc: aspeed: xdma: Add user interface
From: Eddie James
Date: Thu Dec 19 2019 - 11:00:53 EST
On 12/18/19 7:19 PM, Andrew Jeffery wrote:
On Thu, 19 Dec 2019, at 01:39, Eddie James wrote:
This commits adds a miscdevice to provide a user interface to the XDMA
engine. The interface provides the write operation to start DMA
operations. The DMA parameters are passed as the data to the write call.
The actual data to transfer is NOT passed through write. Note that both
directions of DMA operation are accomplished through the write command;
BMC to host and host to BMC.
The XDMA driver reserves an area of physical memory for DMA operations,
as the XDMA engine is restricted to accessing certain physical memory
areas on some platforms. This memory forms a pool from which users can
allocate pages for their usage with calls to mmap. The space allocated
by a client will be the space used in the DMA operation. For an
"upstream" (BMC to host) operation, the data in the client's area will
be transferred to the host. For a "downstream" (host to BMC) operation,
the host data will be placed in the client's memory area.
Poll is also provided in order to determine when the DMA operation is
complete for non-blocking IO.
Signed-off-by: Eddie James <eajames@xxxxxxxxxxxxx>
---
Changes since v2:
- Rework commit message to talk about VGA memory less
- Remove user reset functionality
- Clean up sanity checks in aspeed_xdma_write()
- Wait for transfer complete in the vm area close function
drivers/soc/aspeed/aspeed-xdma.c | 205 ++++++++++++++++++++++++++++++-
1 file changed, 203 insertions(+), 2 deletions(-)
diff --git a/drivers/soc/aspeed/aspeed-xdma.c b/drivers/soc/aspeed/aspeed-xdma.c
index cb94adf798b1..e844937dc925 100644
--- a/drivers/soc/aspeed/aspeed-xdma.c
+++ b/drivers/soc/aspeed/aspeed-xdma.c
@@ -13,6 +13,7 @@
#include <linux/io.h>
#include <linux/jiffies.h>
#include <linux/mfd/syscon.h>
+#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/of_device.h>
@@ -201,6 +202,8 @@ struct aspeed_xdma {
struct clk *clock;
struct reset_control *reset;
+ /* file_lock serializes reads of current_client */
+ struct mutex file_lock;
I wonder whether start_lock can serve this purpose.
/* client_lock protects error and in_progress of the client */
spinlock_t client_lock;
struct aspeed_xdma_client *current_client;
@@ -223,6 +226,8 @@ struct aspeed_xdma {
void __iomem *mem_virt;
dma_addr_t cmdq_phys;
struct gen_pool *pool;
+
+ struct miscdevice misc;
};
struct aspeed_xdma_client {
@@ -522,6 +527,185 @@ static irqreturn_t aspeed_xdma_pcie_irq(int irq,
void *arg)
return IRQ_HANDLED;
}
+static ssize_t aspeed_xdma_write(struct file *file, const char __user *buf,
+ size_t len, loff_t *offset)
+{
+ int rc;
+ struct aspeed_xdma_op op;
+ struct aspeed_xdma_client *client = file->private_data;
+ struct aspeed_xdma *ctx = client->ctx;
+
+ if (len != sizeof(op))
+ return -EINVAL;
+
+ rc = copy_from_user(&op, buf, len);
+ if (rc)
+ return rc;
+
+ if (!op.len || op.len > client->size ||
+ op.direction > ASPEED_XDMA_DIRECTION_UPSTREAM)
+ return -EINVAL;
+
+ if (file->f_flags & O_NONBLOCK) {
+ if (!mutex_trylock(&ctx->file_lock))
+ return -EAGAIN;
+
+ if (ctx->current_client) {
Should be tested under client_lock for consistency with the previous patch,
though perhaps you could use READ_ONCE()?
I think READ_ONCE will work.
+ mutex_unlock(&ctx->file_lock);
+ return -EBUSY;
+ }
+ } else {
+ mutex_lock(&ctx->file_lock);
+
+ rc = wait_event_interruptible(ctx->wait, !ctx->current_client);
+ if (rc) {
+ mutex_unlock(&ctx->file_lock);
+ return -EINTR;
+ }
+ }
+
+ aspeed_xdma_start(ctx, &op, client->phys, client);
+
+ mutex_unlock(&ctx->file_lock);
Shouldn't we lift start_lock out of aspeed_xdma_start() use that here
instead of file_lock? I think that would mean that we could remove
file_lock.
That wouldn't work with the reset though. The reset should hold
start_lock as well, but if a client is waiting here with start_lock,
we'd never get to the reset if the transfer doesn't complete. I think
file_lock is necessary.
+
+ if (!(file->f_flags & O_NONBLOCK)) {
+ rc = wait_event_interruptible(ctx->wait, !client->in_progress);
+ if (rc)
+ return -EINTR;
+
+ if (client->error)
+ return -EIO;
+ }
+
+ return len;
+}
+
+static __poll_t aspeed_xdma_poll(struct file *file,
+ struct poll_table_struct *wait)
+{
+ __poll_t mask = 0;
+ __poll_t req = poll_requested_events(wait);
+ struct aspeed_xdma_client *client = file->private_data;
+ struct aspeed_xdma *ctx = client->ctx;
+
+ if (req & (EPOLLIN | EPOLLRDNORM)) {
+ if (client->in_progress)
+ poll_wait(file, &ctx->wait, wait);
+
+ if (!client->in_progress) {
+ if (client->error)
+ mask |= EPOLLERR;
+ else
+ mask |= EPOLLIN | EPOLLRDNORM;
+ }
+ }
+
+ if (req & (EPOLLOUT | EPOLLWRNORM)) {
+ if (ctx->current_client)
+ poll_wait(file, &ctx->wait, wait);
+
+ if (!ctx->current_client)
+ mask |= EPOLLOUT | EPOLLWRNORM;
+ }
+
+ return mask;
+}
+
+static void aspeed_xdma_vma_close(struct vm_area_struct *vma)
+{
+ int rc;
+ struct aspeed_xdma_client *client = vma->vm_private_data;
+
+ rc = wait_event_interruptible(client->ctx->wait, !client->in_progress);
+ if (rc)
+ return;
+
+ gen_pool_free(client->ctx->pool, (unsigned long)client->virt,
+ client->size);
+
+ client->virt = NULL;
+ client->phys = 0;
+ client->size = 0;
+}
+
+static const struct vm_operations_struct aspeed_xdma_vm_ops = {
+ .close = aspeed_xdma_vma_close,
+};
+
+static int aspeed_xdma_mmap(struct file *file, struct vm_area_struct *vma)
+{
+ int rc;
+ struct aspeed_xdma_client *client = file->private_data;
+ struct aspeed_xdma *ctx = client->ctx;
+
+ /* restrict file to one mapping */
+ if (client->size)
+ return -EBUSY;
+
+ client->size = vma->vm_end - vma->vm_start;
+ client->virt = gen_pool_dma_alloc(ctx->pool, client->size,
+ &client->phys);
+ if (!client->virt) {
+ client->phys = 0;
+ client->size = 0;
+ return -ENOMEM;
+ }
+
+ vma->vm_pgoff = (client->phys - ctx->mem_phys) >> PAGE_SHIFT;
+ vma->vm_ops = &aspeed_xdma_vm_ops;
+ vma->vm_private_data = client;
+ vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+
+ rc = io_remap_pfn_range(vma, vma->vm_start, client->phys >> PAGE_SHIFT,
+ client->size, vma->vm_page_prot);
+ if (rc) {
Probably worth a dev_warn() here so we know what happened?
Sure.
+ gen_pool_free(ctx->pool, (unsigned long)client->virt,
+ client->size);
+
+ client->virt = NULL;
+ client->phys = 0;
+ client->size = 0;
+ return rc;
+ }
+
+ dev_dbg(ctx->dev, "mmap: v[%08lx] to p[%08x], s[%08x]\n",
+ vma->vm_start, (u32)client->phys, client->size);
+
+ return 0;
+}
+
+static int aspeed_xdma_open(struct inode *inode, struct file *file)
+{
+ struct miscdevice *misc = file->private_data;
+ struct aspeed_xdma *ctx = container_of(misc, struct aspeed_xdma, misc);
+ struct aspeed_xdma_client *client = kzalloc(sizeof(*client),
+ GFP_KERNEL);
+
+ if (!client)
+ return -ENOMEM;
+
+ client->ctx = ctx;
+ file->private_data = client;
+ return 0;
+}
+
+static int aspeed_xdma_release(struct inode *inode, struct file *file)
+{
+ struct aspeed_xdma_client *client = file->private_data;
+
+ kfree(client);
I assume the vma gets torn down before release() gets invoked? I haven't
looked closely.
From what I've read, yes, the VMA has to be closed before release() can
be called.
Thanks for the review!
Eddie
Andrew