On 07.12.2015 16:21, kernel@xxxxxxxxxxxxxxxx wrote:
From: Martin Sperl <kernel@xxxxxxxxxxxxxxxx>
This patchset implements a spi-message transformation framework in
SPI-core, that allows drivers to transfor individual spi messages
into something that can more easily get handled by the HW.
This would typically be used for HW which has some limitations on
DMA alignment or max transfer sizes.
This patchset implements at this very moment only splitting
transfers longer than 60k in size into multiple transfers.
Future patches based on this basic patchset:
* split misalligned transfers (there are probably multiple
variations necessary for different HW)
* merge multiple small transfers into a single transfer
The patch-set essentially is based arround spi resource
management on a spi_message basis, which was inspired by
devres.
This framework could also get used to handle spi_unmap_buf
calls with the framework.
Right now the drivers themselves have to implement
spi_master.translate_message, but as soon as the "typical"
HW-variations become apparent this may be reduced to assign
one of a set of "standard" translation methods to
spi_master.translate_message instead, but this may require
some additional parametrization of the HW characteristics.
The whole patch set has been tested successfully on a RPI with:
* spi_loopback_test
* enc28j60
* fb_st7735r - framebuffer playing BigBuckBunny
* mmc-spi with an out of tree patch to work arround the mmc_spi
internal dma mapping issues, that inhibits the driver from working
correctly - this got introduced with commit 0589342c27944e50
("of: set dma_mask to point to coherent_dma_mask")
Martin Sperl (5):
spi: core: added spi_resource management
spi: core: add spi_replace_transfers method
spi: core: add spi_split_transfers_maxsize
spi: core add spi_master.translate_message
spi: bcm2835: make use of the spi_translate_message methods
drivers/spi/spi-bcm2835.c | 31 +++--
drivers/spi/spi.c | 339 +++++++++++++++++++++++++++++++++++++++++++++
include/linux/spi/spi.h | 92 ++++++++++++
3 files changed, 448 insertions(+), 14 deletions(-)
Please note that Patch 1/5 (spi: core: added spi_resource management)
requires that method spi_message_init_no_memset exists(see patch-set
for spi-loopback-test) - this note did not make it into the description
of the second version of this patchset.
In the meantime I have implemented 2 more transformations:
* alignment of buffers (first spi_transfer.tx/rx_buf buffer
remains unaligned, but has spi_transfer.len < alignment,
second spi_transfer is fully alligned for rx/tx_buf with
copying of tx_buf to make it alligned in the case where
rx_buf and tx_buf are misaligned to different offsets)
* merging multiple tiny transfers
One code issue showed up (but that impacted only the new use-cases)
and there was a missing kerneldoc for one of the spi_statistics
members - these are 2 separate patches.
Should I send these separately or do you want a big patchset that
contains all of them?
Here the some of the statistics when running my spi-loopback-test:
==> /sys/class/spi_master/spi32766/statistics/transfers
1588
==> /sys/class/spi_master/spi32766/statistics/transfers_merged
102
==> /sys/class/spi_master/spi32766/statistics/transfers_split_maxsize
160
==> /sys/class/spi_master/spi32766/statistics/transfers_split_unaligned
372
Based on the above I am starting to think of readying a default
implementation for translation that drivers may use:
int spi_translate_message_size_align_merge(
struct spi_master *master, struct spi_message *message)
{
int ret;
/* translate the message */
/* fix alignment of transfers by splitting rx_buf/tx_buf
* (and worsted case copying tx_buf)
*/
ret = spi_split_transfers_unaligned(master, message,
master->min_dma_len,
master->dma_alignment);
if (ret)
return ret;
/* limit transfer length */
if (master->max_dma_len) {
ret = spi_split_transfers_maxsize(master, message,
master->max_dma_len);
if (ret)
return ret;
}
/* merge spi_transfers up to a full page */
ret = spi_merge_transfers(master, message, 2, PAGE_SIZE);
return ret;
}
The spi_master driver would need to set these:
master->translate_message =
spi_translate_message_size_align_merge;
master->min_dma_len = BCM2835_SPI_DMA_MIN_LENGTH;
master->max_dma_len = 15 * PAGE_SIZE;
master->dma_alignment = 4;
As seen above we would need to define a min_dma_len that can get used
as a parameter to align transfers (if a driver is doing PIO for short
transfers, then it makes no sense aligning them in the first place).
This value could also get used in a default implementation of can_dma.
Note that we could also expose min_dma_size via sysfs.
--
To unsubscribe from this list: send the line "unsubscribe linux-spi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
