Messages in this thread | | | From | Piotr Bugalski <> | Date | Thu, 21 Jun 2018 12:52:07 +0200 (CEST) | Subject | Re: [RFC PATCH 0/2] New QuadSPI driver for Atmel SAMA5D2 |
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Hi Boris,
Thank you very much for quick response.
On Wed, 20 Jun 2018, Boris Brezillon wrote:
> Hi Piotr, > > On Mon, 18 Jun 2018 18:21:22 +0200 > Piotr Bugalski <bugalski.piotr@gmail.com> wrote: > >> Hello, >> >> Atmel SAMA5D2 is equipped with two QSPI interfaces. These interfaces can >> work as in SPI-compatible mode or use two / four lines to improve >> communication speed. At the moment there is QSPI driver strongly tied to >> NOR-flash memory and MTD subsystem. >> Intention of this change is to provide new driver which will not be tied >> to MTD and allows using QSPI with NAND-flash memory or other peripherals >> New spi-mem API provides abstraction layer which can disconnect QSPI >> from MTD. This driver doesn't support regular SPI interface, it should >> be used with spi-mem interface only. > > Glad to see that people are starting to convert their SPI NOR > controller drivers to the SPI mem approach. > >> Unfortunately SAMA5D2 hardware by default supports only NOR-flash >> memory. It allows 24- and 32-bit addressing while NAND-flash requires >> 16-bit long. To workaround hardware limitation driver is a bit more >> complicated. >> >> Request to spi-mem contains three fiels: opcode (command), address, >> dummy bytes. SAMA5D2 QSPI hardware supports opcode, address, dummy and >> option byte where address field can only be 24- or 32- bytes long. >> Handling 8-bits long addresses is done using option field. For 16-bits >> address behaviour depends of number of requested dummy bits. If there >> are 8 or more dummy cycles, address is shifted and sent with first dummy >> byte. Otherwise opcode is disabled and first byte of address contains >> command opcode (works only if opcode and address use the same buswidth). >> The limitation is when 16-bit address is used without enough dummy >> cycles and opcode is using different buswidth than address. Other modes >> are supported with described workaround. >> >> It looks like hardware has some limitation in performance. The same issue >> exists in current QSPI driver (MTD/nor-flash) and soft-pack (bare-metal >> library from Atmel). Without using DMA read speed is much worse than >> maximum bandwidth (efficiency 30-40%). Any help with performance >> improvement is highly welcome, especially for NAND-flash memories which >> offers higher capacity than NOR-flash used with previous driver. >> >> Best Regards, >> Piotr >> >> Piotr Bugalski (2): >> spi: Add QuadSPI driver for Atmel SAMA5D2 >> dt-bindings: spi: QuadSPI driver for Atmel SAMA5D2 documentation >> >> .../devicetree/bindings/spi/spi_atmel-qspi.txt | 41 ++ >> drivers/spi/Kconfig | 9 + >> drivers/spi/Makefile | 1 + >> drivers/spi/spi-atmel-qspi.c | 480 +++++++++++++++++++++ > > I'd like a solution where we remove the old driver. I definitely don't > want to have both in parallel. Did you test the new driver with a SPI > NOR to check if it still works correctly? If you did, then I'd suggest > that you add a patch updating defconfigs where the SPI_ATMEL_QUADSPI is > selected and another patch removing the old driver. >
I misunderstood a bit your idea. My main concern was NAND-flash with QSPI interface and I expected original nor-flash driver to stay untouched - at least now. However idea of replacement older driver with spi-mem approach makes a lot of sense to me. I'll test nor-flash with new driver first, it should work but I prefer to be sure. In next version I'll follow your suggestion and replace old nor-flash driver.
>> 4 files changed, 531 insertions(+) >> create mode 100644 Documentation/devicetree/bindings/spi/spi_atmel-qspi.txt > > This should be a simple mv from > Documentation/devicetree/bindings/mtd/atmel-quadspi.txt to > Documentation/devicetree/bindings/spi/spi-atmel-qspi.txt > >> create mode 100644 drivers/spi/spi-atmel-qspi.c >> > > Thanks, > > Boris >
Thank you for comments, Piotr
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