Hi Christophe, Boris Brezillon <[email protected]> wrote on Wed, 7 Nov 2018 13:23:42 +0100:
> On Wed, 7 Nov 2018 12:08:58 +0100 > Christophe Kerello <[email protected]> wrote: > > > >> + > > >> +write_8bit: > > >> + for (i = 0; i < len; i++) > > >> + writeb_relaxed(p[i], io_addr_w); > > > > > > Is 8bit access really enforced by the byte accessor? In this case, how > > > can you be sure 32-bit accesses are doing the right thing? Isn't there > > > a bit somewhere in the config reg to configure the bus width? > > > > > > > I have checked the framework after Miquèl comment sent on v1 => "If you > > selected BOUNCE_BUFFER in the options, buf is supposedly > > aligned, or am I missing something?". > > > > After checking the framework, my understanding was: > > - In case of 8-bit access is requested, the framework provides no > > guarantee on buf. To avoid any issue, I write byte per byte. > > - In case of 8-bit access is not requested, it means that the > > framework will try to write data in the page or in the oob. When writing > > to oob, chip->oob_poi will be used and this buffer is aligned. When > > writing to the page, as the driver enables NAND_USE_BOUNCE_BUFFER > > option, buf is guarantee aligned. > > It's probably what happens right now, but there's no guarantee that all > non-8-bit accesses will be provided a 32-bit aligned buffer. The only > guarantee we provide is on buffer passed to the > chip->ecc.read/write_xxx() hooks, and ->exec_op() can be used outside > of the "page access" path. > > > > > But, I agree that it would be safe to reconfigure the bus width in 8-bit > > before writing byte per byte in case of a 16-bit NAND is used. > > Yes, and I also think you should not base your is-aligned check on the > force_8bit value. Use IS_ALIGNED() instead. Maybe the "configure the bus in 8/16-bit" blocks could deserve a helper. There is probably other locations within this driver with the same logic? Thanks, Miquèl
