Messages in this thread | | | Date | Mon, 18 May 2020 16:19:47 +0100 | From | Mark Brown <> | Subject | Re: [PATCH 2/2] spi: Add Baikal-T1 System Boot SPI Controller driver |
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On Mon, May 18, 2020 at 03:05:42AM +0300, Serge Semin wrote: > On Mon, May 11, 2020 at 10:25:06PM +0100, Mark Brown wrote:
> > Yes, some flags should work here - the issue was that at least some > > controllers may end up trying to do multiple SPI operations for one > > spi-mem thing which will break if the chip select doesn't get changed to > > correspond with what's going on.
> Ok. New SPI flag it is then. It will be something like this: > + #define SPI_CONTROLLER_FLASH_SS BIT(6)
I'd rather use CS than SS (it's more common in the code).
> So, what do you think?
Should be fine, controllers that have an issue implementing just shouldn't set the flag.
> > > > It's not clear to me that this hardware actually supports spi_mem in > > > > hardware?
> > > SPI-mem operations are implemented by means of the EEPROM-read and Tx-only > > > modes of the controller.
> > Sure, but those seem like normal SPI-level things rather than cases > > where the hardware understands that it has a flash attached and is doing > > flash specific things.
> No, hardware can't detect whether the flash is attached. This must be defined by > the platform, like based on the DT sub-nodes.
This isn't about autodetection, it's about the abstraction level the hardware is operating on - some hardware is able to generate flash operations by itself (possibly with some help programming the opcodes that are needed by a given flash), some hardware just works at the bytestream level.
> > A very common case for this stuff is that > > controllers have acceleration blocks for read and fall back on normal > > SPI for writes and erases, that sounds like what's going on here. > > Well, yeah, they do provide some acceleration. EEPROM-read provides automatic > write-cmd-dummy-data-then-read operations. But in this case the only thing we > have to push into the SPI Tx FIFO is command and dummy bytes. The read operation
So it's a write then read but you have to program the write each time? [unhandled content-type:application/pgp-signature] | |