------ Original Message ------
From: "Nico Huber" <[email protected]>
To: "Sean Cross" <[email protected]>; [email protected]
Sent: 22/11/2018 5:28:37 PM
Subject: Re: [flashrom] Raspberry Pi spidev failure
Hi Sean,
1) I'm completely unable to access any SPI chips. This appears to be
due to a bug in the kernel driver, which always yanks the CS line high
despite the cs_change set to 0. A workaround I've come up with is to
do
everything as a single transaction, which seems to fix the problem on
my
device:
what you describe should be impossible, theoretically. CS high means do
nothing. If it stays that way it wouldn't matter if you do everything
in
a single long "do nothing" or in separate shorter ones.
So... how do you sample the CS line?
And at which speed do you run the SPI bus? i.e. the `spispeed`
parameter
to flashrom's linux_spi driver. If you didn't set any, it might just be
too fast.
I've attached a png where I measure both the clock and the CS line.
This is the result of running the command:
./flashrom -c W25Q128.V..M --programmer
linux_spi:dev=/dev/spidev0.0,spispeed=1000
You can see the first 8-bit command gets sent, followed by CS getting
driven high, and then low again when it clocks in the 24-bit response.
Because CS went high, the response came back as all 1s.
With the patch I sent CS does not go high, and so flashrom is able to
work.
2) The other issue is that my device appears to want SPI_MODE_1. When
I
set SPI_MODE_1, it is able to detect and program the board, but fails
to
verify. The image that gets loaded still works, but I'm unsure of
what's causing the issue.
What device is it?
This is a W25Q128JV. The reference manual reports that it should work
with SPI_MODE_0 or SPI_MODE_3, so it's odd that it works only in MODE_1.
I suspect there is something seriously wrong with the Raspberry Pi
kernel here.
Sean
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