-----Original Message----- From: Mike Frysinger [mailto:vapier@gentoo.org] Sent: Thursday, August 27, 2009 2:43 PM To: Hu Mingkai-B21284 Cc: u-boot@lists.denx.de; Fleming Andy-AFLEMING Subject: Re: [U-Boot] [PATCH 3/7] eSPI: add eSPI controller support
On Thursday 27 August 2009 02:27:30 Hu Mingkai-B21284 wrote:
but what if you dont know the length of the transaction ahead of time ? if you look at the spi flash framework, it'll write a few bytes (like the opcode to read the status register) and then it'll just keep reading 1 byte at a
time (polling
the status register). there is no way of knowing the
length ahead
of time. most of the SPI code in u-boot operates this way.
So the driver use the length passed by SPI flash read function. If the length is greater than the max value that is limited by the transaction length register's bitfiled, the driver couldn't read anything.
the length used by the first read covers just the length of the opcode, not any of the data returned by the part
as long as your driver rejects all of these things, it'll be detected at runtime and it should be fine to merge -mike
So the driver combine the opcode length and the data length together, then pass to spi_xfer(for eSPI) . When return the read results, skip the first opcode length bytes.
Thanks, Mingkai