Den 14.12.2017 17.25, skrev David Lechner:
On 12/11/2017 06:45 AM, Noralf Trønnes wrote:
Den 11.12.2017 04.28, skrev David Lechner:
I'm using drm-misc/drm-misc-next and occasionally getting errors as
seen in the stack traces below. I'm not really sure what to make of
it. Any ideas?
I'm starting to wonder if there is some sort of race condition
involved. I only get this warning on some boots, but when I do, it
happens multiple times. Also, when I was debugging a an unrelated
problem, I enabled some of the spin lock checking kernel options that
really slow down the kernel. When I did this, I got this warning all
of the time.
Would it be sensible to allocate a dummy RX buffer once instead of
letting SPI allocate a new one for every transfer?
I have looked at the code and the dummy buffer is needed by some
drivers for DMA transfers. They need both tx and rx buffers to do the
transfer. A solution might be to let tinydrm allocate a dummy rx buffer
and attach it to every spi_transfer.
We could check if it's really needed:
if (spi->controller->flags & (SPI_CONTROLLER_MUST_RX |
SPI_CONTROLLER_MUST_TX))
// allocate dummy rx buffer
And maybe something like this:
+ * @dummy_rx_buf: Optional dummy rx buffer to avoid per transfer
allocation of
+ * dummy rx buffers in the spi core.
int tinydrm_spi_transfer(struct spi_device *spi, u32 speed_hz,
struct spi_transfer *header, u8 bpw, const void *buf,
- size_t len)
+ size_t len, void dummy_rx_buf)
{
struct spi_transfer tr = {
.bits_per_word = bpw,
.speed_hz = speed_hz,
+ .rx_buf = dummy_rx_buf,
};
Noralf.
The spi controller driver has told the spi core to allocate dummy
buffers for tx/rx: spi_sync -> __spi_pump_messages -> spi_map_msg
-> krealloc -> __do_krealloc -> kmalloc_track_caller
order:4 means it's trying to allocate 2^4*PAGE_SIZE = 64kB, which
probably is the max DMA limit. So this is a pixel data transfer.
On my Raspberry Pi I've got 43 chunks of 64kB available if I have
understood this right:
$ sudo cat /proc/buddyinfo
Node 0, zone Normal 40 68 66 51 43 46 13
1 3 3 75
I don't know what those dummy buffers are used for.
Noralf.
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