Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
7671edeb19
To get better performance, current gpmi driver collected and chained all
small DMA transfers in gpmi_nfc_exec_op, the whole chain triggered and
wait for complete at the end.
But some random DMA timeout found in this new driver, with the help of
ftrace, we found the root cause is as follows:
Take gpmi_ecc_read_page() as an example, gpmi_nfc_exec_op collected 6
DMA transfers and the DMA chain triggered at the end. It waits for bch
completion and check jiffies if it's timeout. The typical function graph
shown below,
63.216351 | 1) | gpmi_ecc_read_page() {
63.216352 | 1) 0.750 us | gpmi_bch_layout_std();
63.216354 | 1) | gpmi_nfc_exec_op() {
63.216355 | 1) | gpmi_chain_command() {
63.216356 | 1) | mxs_dma_prep_slave_sg() {
63.216357 | 1) | /* mxs chan ccw idx: 0 */
63.216358 | 1) 1.750 us | }
63.216359 | 1) | mxs_dma_prep_slave_sg() {
63.216360 | 1) | /* mxs chan ccw idx: 1 */
63.216361 | 1) 2.000 us | }
63.216361 | 1) 6.500 us | }
63.216362 | 1) | gpmi_chain_command() {
63.216363 | 1) | mxs_dma_prep_slave_sg() {
63.216364 | 1) | /* mxs chan ccw idx: 2 */
63.216365 | 1) 1.750 us | }
63.216366 | 1) | mxs_dma_prep_slave_sg() {
63.216367 | 1) | /* mxs chan ccw idx: 3 */
63.216367 | 1) 1.750 us | }
63.216368 | 1) 5.875 us | }
63.216369 | 1) | /* gpmi_chain_wait_ready */
63.216370 | 1) | mxs_dma_prep_slave_sg() {
63.216372 | 1) | /* mxs chan ccw idx: 4 */
63.216373 | 1) 3.000 us | }
63.216374 | 1) | /* gpmi_chain_data_read */
63.216376 | 1) | mxs_dma_prep_slave_sg() {
63.216377 | 1) | /* mxs chan ccw idx: 5 */
63.216378 | 1) 2.000 us | }
63.216379 | 1) 1.125 us | mxs_dma_tx_submit();
63.216381 | 1) 1.000 us | mxs_dma_enable_chan();
63.216712 | 0) 2.625 us | mxs_dma_int_handler();
63.216717 | 0) 4.250 us | bch_irq();
63.216723 | 0) 1.250 us | mxs_dma_tasklet();
63.216723 | 1) | /* jiffies left 250 */
63.216725 | 1) ! 372.000 us | }
63.216726 | 1) 2.625 us | gpmi_count_bitflips();
63.216730 | 1) ! 379.125 us | }
but it's not gurantee that bch irq handled always after dma irq handled,
sometimes bch_irq comes first and gpmi_nfc_exec_op won't wait anymore,
another gpmi_nfc_exec_op may get invoked before last DMA chain IRQ
handled, this messed up the next DMA chain and causes DMA timeout. Check
the trace log when issue happened.
63.218923 | 1) | gpmi_ecc_read_page() {
63.218924 | 1) 0.625 us | gpmi_bch_layout_std();
63.218926 | 1) | gpmi_nfc_exec_op() {
63.218927 | 1) | gpmi_chain_command() {
63.218928 | 1) | mxs_dma_prep_slave_sg() {
63.218929 | 1) | /* mxs chan ccw idx: 0 */
63.218929 | 1) 1.625 us | }
63.218931 | 1) | mxs_dma_prep_slave_sg() {
63.218931 | 1) | /* mxs chan ccw idx: 1 */
63.218932 | 1) 1.750 us | }
63.218933 | 1) 5.875 us | }
63.218934 | 1) | gpmi_chain_command() {
63.218934 | 1) | mxs_dma_prep_slave_sg() {
63.218935 | 1) | /* mxs chan ccw idx: 2 */
63.218936 | 1) 1.875 us | }
63.218937 | 1) | mxs_dma_prep_slave_sg() {
63.218938 | 1) | /* mxs chan ccw idx: 3 */
63.218939 | 1) 1.625 us | }
63.218939 | 1) 5.875 us | }
63.218940 | 1) | /* gpmi_chain_wait_ready */
63.218941 | 1) | mxs_dma_prep_slave_sg() {
63.218942 | 1) | /* mxs chan ccw idx: 4 */
63.218942 | 1) 1.625 us | }
63.218943 | 1) | /* gpmi_chain_data_read */
63.218944 | 1) | mxs_dma_prep_slave_sg() {
63.218945 | 1) | /* mxs chan ccw idx: 5 */
63.218947 | 1) 2.375 us | }
63.218948 | 1) 0.625 us | mxs_dma_tx_submit();
63.218949 | 1) 1.000 us | mxs_dma_enable_chan();
63.219276 | 0) 5.125 us | bch_irq(); <----
63.219283 | 1) | /* jiffies left 250 */
63.219285 | 1) ! 358.625 us | }
63.219286 | 1) 2.750 us | gpmi_count_bitflips();
63.219289 | 1) ! 366.000 us | }
63.219290 | 1) | gpmi_ecc_read_page() {
63.219291 | 1) 0.750 us | gpmi_bch_layout_std();
63.219293 | 1) | gpmi_nfc_exec_op() {
63.219294 | 1) | gpmi_chain_command() {
63.219295 | 1) | mxs_dma_prep_slave_sg() {
63.219295 | 0) 1.875 us | mxs_dma_int_handler(); <----
63.219296 | 1) | /* mxs chan ccw idx: 6 */
63.219297 | 1) 2.250 us | }
63.219298 | 1) | mxs_dma_prep_slave_sg() {
63.219298 | 0) 1.000 us | mxs_dma_tasklet();
63.219299 | 1) | /* mxs chan ccw idx: 0 */
63.219300 | 1) 1.625 us | }
63.219300 | 1) 6.375 us | }
63.219301 | 1) | gpmi_chain_command() {
63.219302 | 1) | mxs_dma_prep_slave_sg() {
63.219303 | 1) | /* mxs chan ccw idx: 1 */
63.219304 | 1) 1.625 us | }
63.219305 | 1) | mxs_dma_prep_slave_sg() {
63.219306 | 1) | /* mxs chan ccw idx: 2 */
63.219306 | 1) 1.875 us | }
63.219307 | 1) 6.000 us | }
63.219308 | 1) | /* gpmi_chain_wait_ready */
63.219308 | 1) | mxs_dma_prep_slave_sg() {
63.219309 | 1) | /* mxs chan ccw idx: 3 */
63.219310 | 1) 2.000 us | }
63.219311 | 1) | /* gpmi_chain_data_read */
63.219312 | 1) | mxs_dma_prep_slave_sg() {
63.219313 | 1) | /* mxs chan ccw idx: 4 */
63.219314 | 1) 1.750 us | }
63.219315 | 1) 0.625 us | mxs_dma_tx_submit();
63.219316 | 1) 0.875 us | mxs_dma_enable_chan();
64.224227 | 1) | /* jiffies left 0 */
In the first gpmi_nfc_exec_op, bch_irq comes first and gpmi_nfc_exec_op
exits, but DMA IRQ still not happened yet until the middle of following
gpmi_nfc_exec_op, the first DMA transfer index get messed and DMA get
timeout.
To fix the issue, when there is bch ops in DMA chain, the
gpmi_nfc_exec_op should wait for both completions rather than bch
completion only.
Fixes:
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README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
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Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.