Commit bf15bb38 authored by Michal Schmidt's avatar Michal Schmidt Committed by David S. Miller
Browse files

ice: make writes to /dev/gnssX synchronous 

The current ice driver's GNSS write implementation buffers writes and
works through them asynchronously in a kthread. That's bad because:
 - The GNSS write_raw operation is supposed to be synchronous[1][2].
 - There is no upper bound on the number of pending writes.
   Userspace can submit writes much faster than the driver can process,
   consuming unlimited amounts of kernel memory.

A patch that's currently on review[3] ("[v3,net] ice: Write all GNSS
buffers instead of first one") would add one more problem:
 - The possibility of waiting for a very long time to flush the write
   work when doing rmmod, softlockups.

To fix these issues, simplify the implementation: Drop the buffering,
the write_work, and make the writes synchronous.

I tested this with gpsd and ubxtool.

[1] https://events19.linuxfoundation.org/wp-content/uploads/2017/12/The-GNSS-Subsystem-Johan-Hovold-Hovold-Consulting-AB.pdf
    "User interface" slide.
[2] A comment in drivers/gnss/core.c:gnss_write():
        /* Ignoring O_NONBLOCK, write_raw() is synchronous. */
[3] https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20230217120541.16745-1-karol.kolacinski@intel.com/



Fixes: d6b98c8d ("ice: add write functionality for GNSS TTY")
Signed-off-by: default avatarMichal Schmidt <mschmidt@redhat.com>
Reviewed-by: default avatarSimon Horman <simon.horman@corigine.com>
Tested-by: Sunitha Mekala <sunithax.d.mekala@intel.com> (A Contingent worker at Intel)
Signed-off-by: default avatarTony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d636fc5d

drivers/net/ethernet/intel/ice/ice_common.c

+1 −1
Original line number Diff line number Diff line
@@ -5160,7 +5160,7 @@ ice_aq_read_i2c(struct ice_hw *hw, struct ice_aqc_link_topo_addr topo_addr, 
 */

int

ice_aq_write_i2c(struct ice_hw *hw, struct ice_aqc_link_topo_addr topo_addr,

		 u16 bus_addr, __le16 addr, u8 params, u8 *data,

		 u16 bus_addr, __le16 addr, u8 params, const u8 *data,

		 struct ice_sq_cd *cd)

{

	struct ice_aq_desc desc = { 0 };

drivers/net/ethernet/intel/ice/ice_common.h

+1 −1
Original line number Diff line number Diff line
@@ -229,7 +229,7 @@ ice_aq_read_i2c(struct ice_hw *hw, struct ice_aqc_link_topo_addr topo_addr, 
		struct ice_sq_cd *cd);

int

ice_aq_write_i2c(struct ice_hw *hw, struct ice_aqc_link_topo_addr topo_addr,

		 u16 bus_addr, __le16 addr, u8 params, u8 *data,

		 u16 bus_addr, __le16 addr, u8 params, const u8 *data,

		 struct ice_sq_cd *cd);

bool ice_fw_supports_report_dflt_cfg(struct ice_hw *hw);

#endif /* _ICE_COMMON_H_ */

drivers/net/ethernet/intel/ice/ice_gnss.c

+4 −60
Original line number Diff line number Diff line
@@ -16,8 +16,8 @@ 
 * * number of bytes written - success

 * * negative - error code

 */

static unsigned int

ice_gnss_do_write(struct ice_pf *pf, unsigned char *buf, unsigned int size)

static int

ice_gnss_do_write(struct ice_pf *pf, const unsigned char *buf, unsigned int size)

{

	struct ice_aqc_link_topo_addr link_topo;

	struct ice_hw *hw = &pf->hw;
@@ -72,39 +72,7 @@ ice_gnss_do_write(struct ice_pf *pf, unsigned char *buf, unsigned int size) 
	dev_err(ice_pf_to_dev(pf), "GNSS failed to write, offset=%u, size=%u, err=%d\n",

		offset, size, err);



	return offset;

}



/**

 * ice_gnss_write_pending - Write all pending data to internal GNSS

 * @work: GNSS write work structure

 */

static void ice_gnss_write_pending(struct kthread_work *work)

{

	struct gnss_serial *gnss = container_of(work, struct gnss_serial,

						write_work);

	struct ice_pf *pf = gnss->back;



	if (!pf)

		return;



	if (!test_bit(ICE_FLAG_GNSS, pf->flags))

		return;



	if (!list_empty(&gnss->queue)) {

		struct gnss_write_buf *write_buf = NULL;

		unsigned int bytes;



		write_buf = list_first_entry(&gnss->queue,

					     struct gnss_write_buf, queue);



		bytes = ice_gnss_do_write(pf, write_buf->buf, write_buf->size);

		dev_dbg(ice_pf_to_dev(pf), "%u bytes written to GNSS\n", bytes);



		list_del(&write_buf->queue);

		kfree(write_buf->buf);

		kfree(write_buf);

	}

	return err;

}



/**
@@ -220,8 +188,6 @@ static struct gnss_serial *ice_gnss_struct_init(struct ice_pf *pf) 
	pf->gnss_serial = gnss;



	kthread_init_delayed_work(&gnss->read_work, ice_gnss_read);

	INIT_LIST_HEAD(&gnss->queue);

	kthread_init_work(&gnss->write_work, ice_gnss_write_pending);

	kworker = kthread_create_worker(0, "ice-gnss-%s", dev_name(dev));

	if (IS_ERR(kworker)) {

		kfree(gnss);
@@ -281,7 +247,6 @@ static void ice_gnss_close(struct gnss_device *gdev) 
	if (!gnss)

		return;



	kthread_cancel_work_sync(&gnss->write_work);

	kthread_cancel_delayed_work_sync(&gnss->read_work);

}
@@ -300,10 +265,7 @@ ice_gnss_write(struct gnss_device *gdev, const unsigned char *buf, 
	       size_t count)

{

	struct ice_pf *pf = gnss_get_drvdata(gdev);

	struct gnss_write_buf *write_buf;

	struct gnss_serial *gnss;

	unsigned char *cmd_buf;

	int err = count;



	/* We cannot write a single byte using our I2C implementation. */

	if (count <= 1 || count > ICE_GNSS_TTY_WRITE_BUF)
@@ -319,24 +281,7 @@ ice_gnss_write(struct gnss_device *gdev, const unsigned char *buf, 
	if (!gnss)

		return -ENODEV;



	cmd_buf = kcalloc(count, sizeof(*buf), GFP_KERNEL);

	if (!cmd_buf)

		return -ENOMEM;



	memcpy(cmd_buf, buf, count);

	write_buf = kzalloc(sizeof(*write_buf), GFP_KERNEL);

	if (!write_buf) {

		kfree(cmd_buf);

		return -ENOMEM;

	}



	write_buf->buf = cmd_buf;

	write_buf->size = count;

	INIT_LIST_HEAD(&write_buf->queue);

	list_add_tail(&write_buf->queue, &gnss->queue);

	kthread_queue_work(gnss->kworker, &gnss->write_work);



	return err;

	return ice_gnss_do_write(pf, buf, count);

}



static const struct gnss_operations ice_gnss_ops = {
@@ -432,7 +377,6 @@ void ice_gnss_exit(struct ice_pf *pf) 
	if (pf->gnss_serial) {

		struct gnss_serial *gnss = pf->gnss_serial;



		kthread_cancel_work_sync(&gnss->write_work);

		kthread_cancel_delayed_work_sync(&gnss->read_work);

		kthread_destroy_worker(gnss->kworker);

		gnss->kworker = NULL;

drivers/net/ethernet/intel/ice/ice_gnss.h

+0 −10
Original line number Diff line number Diff line
@@ -22,26 +22,16 @@ 
 */

#define ICE_GNSS_UBX_WRITE_BYTES	(ICE_MAX_I2C_WRITE_BYTES + 1)



struct gnss_write_buf {

	struct list_head queue;

	unsigned int size;

	unsigned char *buf;

};



/**

 * struct gnss_serial - data used to initialize GNSS TTY port

 * @back: back pointer to PF

 * @kworker: kwork thread for handling periodic work

 * @read_work: read_work function for handling GNSS reads

 * @write_work: write_work function for handling GNSS writes

 * @queue: write buffers queue

 */

struct gnss_serial {

	struct ice_pf *back;

	struct kthread_worker *kworker;

	struct kthread_delayed_work read_work;

	struct kthread_work write_work;

	struct list_head queue;

};



#if IS_ENABLED(CONFIG_GNSS)