linux-toradex.git/drivers/tty/serial/amba-pl011.c, branch v5.5-rc7

serial: pl011: Fix DMA ->flush_buffer()

2019-11-18T11:47:06+00:00

PL011's ->flush_buffer() implementation releases and reacquires the port
lock.  Due to a race condition here, data can end up being added to the
circular buffer but neither being discarded nor being sent out.  This
leads to, for example, tcdrain(2) waiting indefinitely.

Process A                       Process B

uart_flush_buffer()
 - acquire lock
 - circ_clear
 - pl011_flush_buffer()
 -- release lock
 -- dmaengine_terminate_all()

                                uart_write()
                                - acquire lock
                                - add chars to circ buffer
                                - start_tx()
                                -- start DMA
                                - release lock

 -- acquire lock
 -- turn off DMA
 -- release lock

                                // Data in circ buffer but DMA is off

According to the comment in the code, the releasing of the lock around
dmaengine_terminate_all() is to avoid a deadlock with the DMA engine
callback.  However, since the time this code was written, the DMA engine
API documentation seems to have been clarified to say that
dmaengine_terminate_all() (in the identically implemented but
differently named dmaengine_terminate_async() variant) does not wait for
any running complete callback to be completed and can even be called
from a complete callback.  So there is no possibility of deadlock if the
DMA engine driver implements this API correctly.

So we should be able to just remove this release and reacquire of the
lock to prevent the aforementioned race condition.

Signed-off-by: Vincent Whitchurch 
Cc: stable 
Link: https://lore.kernel.org/r/20191118092547.32135-1-vincent.whitchurch@axis.com
Signed-off-by: Greg Kroah-Hartman

tty: serial: amba-pl011: Use dma_request_chan() directly for channel request

2019-11-13T13:54:16+00:00

dma_request_slave_channel_reason() is:
#define dma_request_slave_channel_reason(dev, name) \
	dma_request_chan(dev, name)

Signed-off-by: Peter Ujfalusi 
Link: https://lore.kernel.org/r/20191113094618.1725-2-peter.ujfalusi@ti.com
Signed-off-by: Greg Kroah-Hartman

tty/amba-pl011: fix a -Wunused-function warning

2019-10-04T12:58:05+00:00

pl011_dma_probe() is only used in pl011_dma_startup() which does only
exist when CONFIG_DMA_ENGINE=y, so remove the unused dummy version to
silence the warning.

Signed-off-by: Qian Cai 
Link: https://lore.kernel.org/r/1568726340-4518-1-git-send-email-cai@lca.pw
Signed-off-by: Greg Kroah-Hartman

tty: Remove dev_err() usage after platform_get_irq()

2019-09-04T10:43:49+00:00

We don't need dev_err() messages when platform_get_irq() fails now that
platform_get_irq() prints an error message itself when something goes
wrong. Let's remove these prints with a simple semantic patch.

// 
@@
expression ret;
struct platform_device *E;
@@

ret =
(
platform_get_irq(E, ...)
|
platform_get_irq_byname(E, ...)
);

if ( \( ret < 0 \| ret <= 0 \) )
{
(
-if (ret != -EPROBE_DEFER)
-{ ...
-dev_err(...);
-... }
|
...
-dev_err(...);
)
...
}
// 

While we're here, remove braces on if statements that only have one
statement (manually).

Cc: Greg Kroah-Hartman 
Cc: Jiri Slaby 
Cc: Greg Kroah-Hartman 
Signed-off-by: Stephen Boyd 
Link: https://lore.kernel.org/r/20190730181557.90391-45-swboyd@chromium.org
Signed-off-by: Greg Kroah-Hartman

tty: amba-pl011: allow shared interrupt

2019-05-21T10:12:03+00:00

The PL011 register space includes all necessary status bits to
determine whether a device instance requires handling in response
to an interrupt. Therefore, multiple instances of the device could
be serviced by a single shared interrupt, which is the case on BCM7211.

Signed-off-by: Doug Berger 
Signed-off-by: Florian Fainelli 
Signed-off-by: Greg Kroah-Hartman

serial: set suppress_bind_attrs flag only if builtin

2018-11-09T17:07:17+00:00

When the test 'CONFIG_DEBUG_TEST_DRIVER_REMOVE=y' is enabled,
arch_initcall(pl011_init) came before subsys_initcall(default_bdi_init).
devtmpfs gets killed because we try to remove a file and decrement the
wb reference count before the noop_backing_device_info gets initialized.

[    0.332075] Serial: AMBA PL011 UART driver
[    0.485276] 9000000.pl011: ttyAMA0 at MMIO 0x9000000 (irq = 39, base_baud = 0) is a PL011 rev1
[    0.502382] console [ttyAMA0] enabled
[    0.515710] Unable to handle kernel paging request at virtual address 0000800074c12000
[    0.516053] Mem abort info:
[    0.516222]   ESR = 0x96000004
[    0.516417]   Exception class = DABT (current EL), IL = 32 bits
[    0.516641]   SET = 0, FnV = 0
[    0.516826]   EA = 0, S1PTW = 0
[    0.516984] Data abort info:
[    0.517149]   ISV = 0, ISS = 0x00000004
[    0.517339]   CM = 0, WnR = 0
[    0.517553] [0000800074c12000] user address but active_mm is swapper
[    0.517928] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[    0.518305] Modules linked in:
[    0.518839] CPU: 0 PID: 13 Comm: kdevtmpfs Not tainted 4.19.0-rc5-next-20180928-00002-g2ba39ab0cd01-dirty #82
[    0.519307] Hardware name: linux,dummy-virt (DT)
[    0.519681] pstate: 80000005 (Nzcv daif -PAN -UAO)
[    0.519959] pc : __destroy_inode+0x94/0x2a8
[    0.520212] lr : __destroy_inode+0x78/0x2a8
[    0.520401] sp : ffff0000098c3b20
[    0.520590] x29: ffff0000098c3b20 x28: 00000000087a3714
[    0.520904] x27: 0000000000002000 x26: 0000000000002000
[    0.521179] x25: ffff000009583000 x24: 0000000000000000
[    0.521467] x23: ffff80007bb52000 x22: ffff80007bbaa7c0
[    0.521737] x21: ffff0000093f9338 x20: 0000000000000000
[    0.522033] x19: ffff80007bbb05d8 x18: 0000000000000400
[    0.522376] x17: 0000000000000000 x16: 0000000000000000
[    0.522727] x15: 0000000000000400 x14: 0000000000000400
[    0.523068] x13: 0000000000000001 x12: 0000000000000001
[    0.523421] x11: 0000000000000000 x10: 0000000000000970
[    0.523749] x9 : ffff0000098c3a60 x8 : ffff80007bbab190
[    0.524017] x7 : ffff80007bbaa880 x6 : 0000000000000c88
[    0.524305] x5 : ffff0000093d96c8 x4 : 61c8864680b583eb
[    0.524567] x3 : ffff0000093d6180 x2 : ffffffffffffffff
[    0.524872] x1 : 0000800074c12000 x0 : 0000800074c12000
[    0.525207] Process kdevtmpfs (pid: 13, stack limit = 0x(____ptrval____))
[    0.525529] Call trace:
[    0.525806]  __destroy_inode+0x94/0x2a8
[    0.526108]  destroy_inode+0x34/0x88
[    0.526370]  evict+0x144/0x1c8
[    0.526636]  iput+0x184/0x230
[    0.526871]  dentry_unlink_inode+0x118/0x130
[    0.527152]  d_delete+0xd8/0xe0
[    0.527420]  vfs_unlink+0x240/0x270
[    0.527665]  handle_remove+0x1d8/0x330
[    0.527875]  devtmpfsd+0x138/0x1c8
[    0.528085]  kthread+0x14c/0x158
[    0.528291]  ret_from_fork+0x10/0x18
[    0.528720] Code: 92800002 aa1403e0 d538d081 8b010000 (c85f7c04)
[    0.529367] ---[ end trace 5a3dee47727f877c ]---

Rework to set suppress_bind_attrs flag to avoid removing the device when
CONFIG_DEBUG_TEST_DRIVER_REMOVE=y. This applies for pic32_uart and
xilinx_uartps as well.

Co-developed-by: Arnd Bergmann 
Signed-off-by: Arnd Bergmann 
Signed-off-by: Anders Roxell 
Signed-off-by: Greg Kroah-Hartman

tty: pl011: Avoid spuriously stuck-off interrupts

2018-05-14T11:41:05+00:00

Commit 9b96fbacda34 ("serial: PL011: clear pending interrupts")
clears the RX and receive timeout interrupts on pl011 startup, to
avoid a screaming-interrupt scenario that can occur when the
firmware or bootloader leaves these interrupts asserted.

This has been noted as an issue when running Linux on qemu [1].

Unfortunately, the above fix seems to lead to potential
misbehaviour if the RX FIFO interrupt is asserted _non_ spuriously
on driver startup, if the RX FIFO is also already full to the
trigger level.

Clearing the RX FIFO interrupt does not change the FIFO fill level.
In this scenario, because the interrupt is now clear and because
the FIFO is already full to the trigger level, no new assertion of
the RX FIFO interrupt can occur unless the FIFO is drained back
below the trigger level.  This never occurs because the pl011
driver is waiting for an RX FIFO interrupt to tell it that there is
something to read, and does not read the FIFO at all until that
interrupt occurs.

Thus, simply clearing "spurious" interrupts on startup may be
misguided, since there is no way to be sure that the interrupts are
truly spurious, and things can go wrong if they are not.

This patch instead clears the interrupt condition by draining the
RX FIFO during UART startup, after clearing any potentially
spurious interrupt.  This should ensure that an interrupt will
definitely be asserted if the RX FIFO subsequently becomes
sufficiently full.

The drain is done at the point of enabling interrupts only.  This
means that it will occur any time the UART is newly opened through
the tty layer.  It will not apply to polled-mode use of the UART by
kgdboc: since that scenario cannot use interrupts by design, this
should not matter.  kgdboc will interact badly with "normal" use of
the UART in any case: this patch makes no attempt to paper over
such issues.

This patch does not attempt to address the case where the RX FIFO
fills faster than it can be drained: that is a pathological
hardware design problem that is beyond the scope of the driver to
work around.  As a failsafe, the number of poll iterations for
draining the FIFO is limited to twice the FIFO size.  This will
ensure that the kernel at least boots even if it is impossible to
drain the FIFO for some reason.

[1] [Qemu-devel] [Qemu-arm] [PATCH] pl011: do not put into fifo
before enabled the interruption
https://lists.gnu.org/archive/html/qemu-devel/2018-01/msg06446.html

Reported-by: Wei Xu 
Cc: Russell King 
Cc: Linus Walleij 
Cc: Peter Maydell 
Fixes: 9b96fbacda34 ("serial: PL011: clear pending interrupts")
Signed-off-by: Dave Martin 
Cc: stable 
Tested-by: Wei Xu 
Signed-off-by: Greg Kroah-Hartman

serial: pl011: Use cached copy of IMSC register

2017-11-28T14:35:51+00:00

Commit 075167ed71b7 ("drivers: PL011: replace UART_MIS reading with
_RIS & _IMSC") amended this driver's interrupt handler to read the
Raw Interrupt Status (RIS) and Interrupt Mask Set/Clear (IMSC) registers
instead of the Masked Interrupt Status (MIS) register.  The change was
made to attain compatibility with SBSA UARTs which lack the MIS register.

However the IMSC register is cached by the driver.  Using the cached
copy saves one register read per interrupt.

I've tested this change successfully on a BCM2837 (Raspberry Pi CM3).

Cc: Mathias Duckeck 
Cc: Phil Elwell 
Cc: Stefan Wahren 
Cc: Andre Przywara 
Cc: Mark Langsdorf 
Cc: Naresh Bhat 
Cc: Russell King 
Signed-off-by: Lukas Wunner 
Signed-off-by: Greg Kroah-Hartman

serial: pl011: Drop duplicate loop counter

2017-11-28T14:32:33+00:00

pl011_fifo_to_tty() has two counters (max_count and fifotaken) for the
same loop.  One counter should suffice.  This saves one subtraction per
character read from the RX FIFO.

Cc: Mathias Duckeck 
Cc: Phil Elwell 
Cc: Stefan Wahren 
Cc: Linus Walleij 
Cc: Russell King 
Signed-off-by: Lukas Wunner 
Signed-off-by: Greg Kroah-Hartman

tty: serial: Remove redundant license text

2017-11-08T12:08:12+00:00

Now that the SPDX tag is in all tty files, that identifies the license
in a specific and legally-defined manner.  So the extra GPL text wording
can be removed as it is no longer needed at all.

This is done on a quest to remove the 700+ different ways that files in
the kernel describe the GPL license text.  And there's unneeded stuff
like the address (sometimes incorrect) for the FSF which is never
needed.

No copyright headers or other non-license-description text was removed.

Cc: Jiri Slaby 
Cc: Eric Anholt 
Cc: Stefan Wahren 
Cc: Florian Fainelli 
Cc: Ray Jui 
Cc: Scott Branden 
Cc: bcm-kernel-feedback-list@broadcom.com
Cc: "James E.J. Bottomley" 
Cc: Helge Deller 
Cc: Joachim Eastwood 
Cc: Matthias Brugger 
Cc: Masahiro Yamada 
Cc: Tobias Klauser 
Cc: Russell King 
Cc: Vineet Gupta 
Cc: Richard Genoud 
Cc: Alexander Shiyan 
Cc: Baruch Siach 
Cc: Pat Gefre 
Cc: "Guilherme G. Piccoli" 
Cc: Jason Wessel 
Cc: Vladimir Zapolskiy 
Cc: Sylvain Lemieux 
Cc: Carlo Caione 
Cc: Kevin Hilman 
Cc: Liviu Dudau 
Cc: Sudeep Holla 
Cc: Lorenzo Pieralisi 
Cc: Andy Gross 
Cc: David Brown 
Cc: "Andreas Färber" 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Michael Ellerman 
Cc: Kevin Cernekee 
Cc: Laxman Dewangan 
Cc: Thierry Reding 
Cc: Jonathan Hunter 
Cc: Barry Song 
Cc: Patrice Chotard 
Cc: Maxime Coquelin 
Cc: Alexandre Torgue 
Cc: Chris Metcalf 
Cc: Peter Korsgaard 
Cc: Timur Tabi 
Cc: Tony Prisk 
Cc: Michal Simek 
Cc: "Sören Brinkmann" 
Signed-off-by: Greg Kroah-Hartman