RE: [PATCH v5 1/5] spi: spi-mem: Add driver for NXP FlexSPI controller

[Yogesh Narayan Gaur]

Hi Boris,

> -----Original Message-----
> From: Boris Brezillon [mailto:boris.brezillon@xxxxxxxxxxx]
> Sent: Monday, December 10, 2018 4:39 PM
> To: Yogesh Narayan Gaur <yogeshnarayan.gaur@xxxxxxx>
> Cc: Schrempf Frieder <frieder.schrempf@xxxxxxxxxx>; linux-
> mtd@xxxxxxxxxxxxxxxxxxx; marek.vasut@xxxxxxxxx; broonie@xxxxxxxxxx; linux-
> spi@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; robh@xxxxxxxxxx;
> mark.rutland@xxxxxxx; shawnguo@xxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; computersforpeace@xxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v5 1/5] spi: spi-mem: Add driver for NXP FlexSPI controller
> 
> On Mon, 10 Dec 2018 10:59:54 +0000
> Yogesh Narayan Gaur <yogeshnarayan.gaur@xxxxxxx> wrote:
> 
> > Hi Boris,
> >
> > > -----Original Message-----
> > > From: Boris Brezillon [mailto:boris.brezillon@xxxxxxxxxxx]
> > > Sent: Monday, December 10, 2018 4:20 PM
> > > To: Yogesh Narayan Gaur <yogeshnarayan.gaur@xxxxxxx>
> > > Cc: Schrempf Frieder <frieder.schrempf@xxxxxxxxxx>; linux-
> > > mtd@xxxxxxxxxxxxxxxxxxx; marek.vasut@xxxxxxxxx; broonie@xxxxxxxxxx;
> > > linux- spi@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx;
> > > robh@xxxxxxxxxx; mark.rutland@xxxxxxx; shawnguo@xxxxxxxxxx;
> > > linux-arm- kernel@xxxxxxxxxxxxxxxxxxx; computersforpeace@xxxxxxxxx;
> > > linux- kernel@xxxxxxxxxxxxxxx
> > > Subject: Re: [PATCH v5 1/5] spi: spi-mem: Add driver for NXP FlexSPI
> > > controller
> > >
> > > On Mon, 10 Dec 2018 10:43:56 +0000
> > > Yogesh Narayan Gaur <yogeshnarayan.gaur@xxxxxxx> wrote:
> > >
> > > > > > Thus, in LUT preparation we have assigned only the base address.
> > > > > > Now if I have assigned ahb_buf_size to FSPI_FLSHXXCR0 register
> > > > > > then for
> > > > > read/write data beyond limit of ahb_buf_size offset I get data corruption.
> > > > >
> > > > > Why would you do that? We have the ->adjust_op_size() exactly
> > > > > for this reason, so, if someone tries to do a spi_mem_op with
> > > > > data.nbytes > ahb_buf_size you should return an error.
> > > > >
> > > > Let me explain my implementation with example. If I have to write
> > > > data of size
> > > 0x100 bytes at offset 0x1200 for CS1, I would program as below:
> > > > In func nxp_fspi_select_mem(), would set value of controller
> > > > address space
> > > size, memmap_phy_size, to FSPI_FLSHA2CR0 and rest all FSPI_FLSHXXCR0 as
> 0.
> > > > Value of memmap_phy_size is 0x10000000 i.e. 256 MB for my
> > > > LX2160ARDB
> > > target.
> > > > Then in nxp_fspi_prepare_lut(), I would prepare LUT ADDR with
> > > > address length
> > > requirement 3/4 byte for NOR or 1/2/3/4 bytes for NAND flash.
> > > > Also for LUT_NXP_WRITE would program data bytes as 0.
> > > >
> > > > Then inside func nxp_fspi_do_op(), set register FSPI_IPCR0 as the
> > > > address offset i.e. 0x1200 and in register FSPI_IPCR1 program the
> > > > data size to write i.e. 0x100
> > > >
> > > > If, as suggested if I tries to mark value of register
> > > > FSPI_FLSHA2CR0 equal to
> > > ahb_buf_size (0x800), then access for address 0x1200 gives me wrong
> > > data. This is because as per the controller specification access to
> > > flash connected at CS1 can be performed under range of FSPI_ FLSHA1CR0
> and FSPI_ FLSHA2CR0.
> > >
> > > Don't you have a way to set an offset to apply to the address
> > > accessed through the AHB? And if you don't, how will it work if your
> > > mapping is smaller than the flash size?
> >
> > Write operations are triggered using IP commands instead of AHB command.
> > For Read AHB command is used and in this we are adding the offset when
> performing memcpy_fromIO operation
> >       memcpy_fromio(op->data.buf.in, (f->ahb_addr + op->addr.val),
> > len);
> >
> > AHB/IP operations are independent of the way how CS got selected. CS
> selection depends, e.g. CS1 on the value of register FSPI_FLSHA1CR0 and
> FSPI_FLSHA2CR0.
> >
> > Mapping can never going to be smaller than the connected flash size as per
> discussion with the Board design team and if it's possible by user manually
> changes the non-soldered part then flash area beyond complete mapping is not
> accessible.
> > On LX2160ARDB, with mapping of 256MB, for now we are having 4 flash
> devices connected with size as 64 MB. If user wants he can have only one single
> flash with flash size of 256MB.
> 
> Given that the dirmap interface has now been merged and the MTD side of
> things is soon to be merged, I'd recommend you to implement it in your
> v6 and only use non-AHB accesses for the ->exec_op() implementation.

This would going to be performance hit if I would use non-AHB accesses for ->exec_op().
In read in v5 I am using AHB mode for read if read data size is greater than rxfifo size and if its less than rxfifo then use IP mode for read.

--
Regards
Yogesh Gaur