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DMA on this hardware is limited to dealing with a 4096 bytes at a
time. Previously, the driver was set up accordingly to request single-page
DMA buffers, however that had the effect of generating a large number
of small MMC requests for data I/O.
Improve the driver to accept multi-entry scatter-gather lists. The size of
each entry is already capped to 4096 bytes (AU6601_MAX_DMA_BLOCK_SIZE),
matching the hardware requirements. Existing driver code already iterates
through remaining sglist entries after each DMA transfer is complete.
Also add some comments to help clarify the situation, and clear up
some of the confusion I had regarding DMA vs PIO.
Testing with dd, this increases write performance from 2mb/sec to
10mb/sec, and increases read performance from 4mb/sec to 14mb/sec.
Signed-off-by: Daniel Drake <drake@endlessm.com>
Link: http://lkml.kernel.org/r/CAD8Lp47JYdZzbV9F+asNwvSfLF_po_J7ir6R_Vb-Dab21_=Krw@mail.gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
This reverts commit 57ebb96c293da9f0ec56aba13c5541269a5c10b1.
Usage of the DMA page iterator was problematic here because
we were not considering offset & length of entries in the scatterlist.
Also, after further discussion, the suggested revised approach is much
more similar to the driver implementation before this commit was
applied, so revert it.
Signed-off-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
DMA on this hardware is limited to dealing with a single page at a
time. Previously, the driver was set up accordingly to request single-page
DMA buffers, however that had the effect of generating a large number
of small MMC requests for data I/O.
Improve the driver to accept scatter-gather DMA buffers of larger sizes.
Iterate through those buffers a page at a time.
Testing with dd, this increases write performance from 2mb/sec to
10mb/sec, and increases read performance from 4mb/sec to 14mb/sec.
Signed-off-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Enable the DMA codepath for writes as well as reads.
This improves write speed from 1mb/sec to 2mb/sec (tested with dd).
The original ampe_stor vendor driver also uses DMA for writes.
Signed-off-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
The alcor driver is setting up data transfer and submitting the associated
MMC command at the same time. While this works most of the time, it
occasionally causes problems upon write.
In the working case, after setting up the data transfer and submitting
the MMC command, an interrupt comes in a moment later with CMD_END and
WRITE_BUF_RDY bits set. The data transfer then happens without problem.
However, on occasion, the interrupt that arrives at that point only
has WRITE_BUF_RDY set. The hardware notifies that it's ready to write
data, but the associated MMC command is still running. Regardless, the
driver was proceeding to write data immediately, and that would then cause
another interrupt indicating data CRC error, and the write would fail.
Additionally, the transfer setup function alcor_trigger_data_transfer()
was being called 3 times for each write operation, which was confusing
and may be contributing to this issue.
Solve this by tweaking the driver behaviour to follow the sequence observed
in the original ampe_stor vendor driver:
1. When starting request handling, write 0 to DATA_XFER_CTRL
2. Submit the command
3. Wait for CMD_END interrupt and then trigger data transfer
4. For the PIO case, trigger the next step of the data transfer only
upon the following DATA_END interrupt, which occurs after the block has
been written.
I confirmed that the read path still works (DMA & PIO) and also now
presents more consistency with the operations performed by ampe_stor.
Signed-off-by: Daniel Drake <drake@endlessm.com>
Fixes: c5413ad815 ("mmc: add new Alcor Micro Cardreader SD/MMC driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Setting max_blk_count to 1 here was causing the mmc block layer
to always use the MMC_READ_SINGLE_BLOCK command here, which the
driver does not DMA-accelerate.
Drop the max_blk_ settings here. The mmc host defaults suffice,
along with the max_segs and max_seg_size settings, which I have
now documented in more detail.
Now each MMC command reads 4 512-byte blocks, using DMA instead of
PIO. On my SD card, this increases read performance (measured with dd)
from 167kb/sec to 4.6mb/sec.
Link: http://lkml.kernel.org/r/CAD8Lp47L5T3jnAjBiPs1cQ+yFA3L6LJtgFvMETnBrY63-Zdi2g@mail.gmail.com
Signed-off-by: Daniel Drake <drake@endlessm.com>
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>
Fixes: c5413ad815 ("mmc: add new Alcor Micro Cardreader SD/MMC driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Fixes gcc '-Wunused-but-set-variable' warning:
drivers/mmc/host/alcor.c: In function 'alcor_data_set_dma':
drivers/mmc/host/alcor.c:124:12: warning:
variable 'len' set but not used [-Wunused-but-set-variable]
drivers/mmc/host/alcor.c:648:15: warning:
variable 'clock_out' set but not used [-Wunused-but-set-variable]
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
This driver provides support for Alcor Micro AU6601 and AU6621
SD/MMC controller.
Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
