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

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Date:   Mon, 10 Dec 2018 12:03:59 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Yogesh Narayan Gaur <yogeshnarayan.gaur@....com>
Cc:     Schrempf Frieder <frieder.schrempf@...tron.de>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "marek.vasut@...il.com" <marek.vasut@...il.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "robh@...nel.org" <robh@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "computersforpeace@...il.com" <computersforpeace@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
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@....com> wrote:

> Hi Boris,
> 
> > -----Original Message-----
> > From: Boris Brezillon [mailto:boris.brezillon@...tlin.com]
> > Sent: Monday, December 10, 2018 4:20 PM
> > To: Yogesh Narayan Gaur <yogeshnarayan.gaur@....com>
> > Cc: Schrempf Frieder <frieder.schrempf@...tron.de>; linux-
> > mtd@...ts.infradead.org; marek.vasut@...il.com; broonie@...nel.org; linux-
> > spi@...r.kernel.org; devicetree@...r.kernel.org; robh@...nel.org;
> > mark.rutland@....com; shawnguo@...nel.org; linux-arm-
> > kernel@...ts.infradead.org; computersforpeace@...il.com; linux-
> > kernel@...r.kernel.org
> > 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@....com> 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.

How unfortunate is that, especially when all that was required was an
extra reg to specify a "flash_offset" to apply to the address passed by
the AHB logic.