[Cbe-oss-dev] [patch 3/5] cell: updated driver for DDR2 memory on AXON

[Arnd Bergmann]

On Tuesday 26 June 2007, Christophe Lamoureux wrote:
> 
> > +/**
> > + * axon_ram_direct_access - direct_access() method for block device
> > + * @device, @sector, @data: see block_device_operations method
> > + */
> > +static int
> > +axon_ram_direct_access(struct block_device *device, sector_t sector,
> > + unsigned long *data)
> > +{
> > + struct axon_ram_bank *bank = device->bd_disk->private_data;
> > + loff_t offset;
> > +
> > + offset = sector << AXON_RAM_SECTOR_SHIFT;
> > + if (offset >= bank->size) {
> > + dev_err(&bank->device->dev, "Access outside of address space\n");
> > + return -ERANGE;
> > + }
> > +
> > + *data = bank->ph_addr + offset;
> > +
> > + return 0;
> > +}
> 
> By looking the ext2 implementation in 2.6.21 and doing some trials ( this is 
> the only file-system that looks to use the direct_access method of block 
> device )  I do not understand how this direct access function ( 
> axon_ram_direct_access ) implementation could work. 
> 
> The value of *data returned is a physical address of the DDR as seen from the 
> PPU ( something like 0x100_0000_0000+ offset )
> 
> The method ext2_clear_xip_target() will call clear_page() with this physical 
> address. This does not work. 
> 
> There is the same kind of issue later in method ext2_get_xip_page() with 
> virt_to_page() with the physical address. 
> 
> Note, that if the line 
> 
> 	*data = bank->ph_addr + offset;
> 
> in axon_ram_direct_access is changed to
> 
> 	*data = bank->io_addr + offset; 
> 
> the issue in ext2_clear_xip_target()  --> clear_page() would be corrected but 
> the  ext2_get_xip_page() --> virt_to_page() would not work as the virtual 
> address given would be the result of a ioremap_flags(). 
> 
> Did I misunderstood or miss something ? 

From looking at the code, I'd say you are right. Maxim, could you give Christoph
some insight on this?

	Arnd <><