[coreboot] [PATCH]Remove non-CBFS
peter at stuge.se
Thu Oct 1 00:43:33 CEST 2009
ron minnich wrote:
> can anyone even buy an m57sli any more?
No, they are out of production and out of stock really everywhere.
> Was it an unfortunate mistake -- never repeated -- that FLASH was
> not directly accessible?
In the long term (a few years) the problem will go away as SPI
masters move into every chipset, but as long as boards are using
extra components between the CPU and the flash chip, there can be
issues like this.
> If the m57sli is an exception and we'll never see this problem
> again, I say we drop it. Copying all of flash into ram sounds bad.
It would be unfortunate to drop support for one of the most hack
friendly boards that we've seen in a while.
> But FLASH is so slow I doubt that the cost of an accessor function
> is going to kill us. Function calls run in nanoseconds, and if SPI
> really is only 40 MB/sec., then that's 25 ns/byte.
40 Mbyte/s seems way optimistic to me. In the ideal case it's
possible to stream all of the data out of the chip without overhead,
and even then it's CLK/8 Mbyte/s. I think the fastest CLK I've seen
recently is 90 MHz but the superio SPI masters only run at 16 MHz.
(=2Mbyte/s assuming no overhead, which is far from the norm, it's
common to have several bytes overhead for each 256 bytes of data)
Chipsets could run faster, but not all flash chips can run super fast
either. 25-33 somewhere would be the safe number. Max CLK seems to
increase with size and each flash chip product generation though.
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