bf15bb38ec
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: d6b98c8d24 ("ice: add write functionality for GNSS TTY")
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Tested-by: Sunitha Mekala <sunithax.d.mekala@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
49 lines
1.6 KiB
C
49 lines
1.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/* Copyright (C) 2021-2022, Intel Corporation. */
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#ifndef _ICE_GNSS_H_
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#define _ICE_GNSS_H_
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#define ICE_E810T_GNSS_I2C_BUS 0x2
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#define ICE_GNSS_POLL_DATA_DELAY_TIME (HZ / 50) /* poll every 20 ms */
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#define ICE_GNSS_TIMER_DELAY_TIME (HZ / 10) /* 0.1 second per message */
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#define ICE_GNSS_TTY_WRITE_BUF 250
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#define ICE_MAX_I2C_DATA_SIZE FIELD_MAX(ICE_AQC_I2C_DATA_SIZE_M)
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#define ICE_MAX_I2C_WRITE_BYTES 4
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/* u-blox ZED-F9T specific definitions */
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#define ICE_GNSS_UBX_I2C_BUS_ADDR 0x42
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/* Data length register is big endian */
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#define ICE_GNSS_UBX_DATA_LEN_H 0xFD
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#define ICE_GNSS_UBX_DATA_LEN_WIDTH 2
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#define ICE_GNSS_UBX_EMPTY_DATA 0xFF
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/* For u-blox writes are performed without address so the first byte to write is
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* passed as I2C addr parameter.
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*/
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#define ICE_GNSS_UBX_WRITE_BYTES (ICE_MAX_I2C_WRITE_BYTES + 1)
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/**
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* struct gnss_serial - data used to initialize GNSS TTY port
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* @back: back pointer to PF
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* @kworker: kwork thread for handling periodic work
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* @read_work: read_work function for handling GNSS reads
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*/
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struct gnss_serial {
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struct ice_pf *back;
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struct kthread_worker *kworker;
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struct kthread_delayed_work read_work;
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};
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#if IS_ENABLED(CONFIG_GNSS)
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void ice_gnss_init(struct ice_pf *pf);
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void ice_gnss_exit(struct ice_pf *pf);
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bool ice_gnss_is_gps_present(struct ice_hw *hw);
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#else
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static inline void ice_gnss_init(struct ice_pf *pf) { }
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static inline void ice_gnss_exit(struct ice_pf *pf) { }
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static inline bool ice_gnss_is_gps_present(struct ice_hw *hw)
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{
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return false;
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}
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#endif /* IS_ENABLED(CONFIG_GNSS) */
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#endif /* _ICE_GNSS_H_ */
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