optimizing the nand read performance by reducing interrupts from 4 to 1

Sam Lefebvre sam.lefebvre at essensium.com
Thu Apr 26 08:41:21 PDT 2018

The current implementation for gmpi nand flashes use existing libraries for composing                    
dma command chains in different pieces with mutliple interrupts. This invokes a lot of                   
unnecessary context switches. In order to make more optimal use of dma chaining capabilities
of the gpmi hardware, some rework must be performed to allow gpmi_ecc_read_page() 
and gpmi_ecc_read_subpage() submitting a range of dma's to reduce the interrupts from 
4 to 1 for every page read.

In the current situation, a page read for large page incurs 4 interrupts:
- DMA for READ0
- DMA for reading of page data
This series is based on a previous post and contains some optimizations in the commits.
The changes in nand_command() and nand_command_lp() are omitted and commits are re-ordered
in such way that the changes for reducing the interrupts are moved to the end.

In order to do the preparation of this work, ready/busy signalling is aggregated and
error handling in gpmi_ecc_read_oob() has been reviewed.            

Some changes by Sasha Hauer are also adopted which contain some bugfixes and preliminary
cleanup of several parts in de code.

Sam lefebvre 

Arnout Vandecappelle (Essensium/Mind) (2):
      mtd: rawnand: gpmi: instantiate cmdfunc
      mtd: rawnand: gpmi: gpmi_nand_command(): simplification and formatting

Sam Lefebvre (5):
      mtd: rawnand: gpmi: set aggregate ready/busy signalling
      mtd: rawnand: gpmi: return generated errors in gpmi_ecc_read_oob()
      mtd: rawnand: gpmi: poll the BCH interrupt bit in start_dma_with_bch_irq()
      mtd: rawnand: gpmi: issue two commands in a single DMA chain
      mtd: rawnand: gmpi: chain gpmi_nand_command() with gpmi_ecc_read_page_data()

Sascha Hauer (6):
      mtd: nand: gpmi: drop dma_ops_type
      mtd: nand: gpmi: pass buffer and len around
      mtd: nand: gpmi: put only once used functions inline
      mtd: nand: gpmi: remove direct_dma_map_ok from driver data struct
      mtd: nand: gpmi: return valid value from bch_set_geometry()
      mtd: nand: gpmi: remove unnecessary variables

 drivers/dma/mxs-dma.c                      |   3 +
 drivers/mtd/nand/raw/gpmi-nand/gpmi-lib.c  |  77 ++++---
 drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c | 359 ++++++++++++++++-------------
 drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.h |  37 ++-
 drivers/mtd/nand/raw/gpmi-nand/gpmi-regs.h |   1 +
 5 files changed, 260 insertions(+), 217 deletions(-)

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