According to documentation, there must be at least one cycle delay
between two consecutive writes of the DR register. Apparently, this is
true for reading too, though undocumented.
The read_dr() inline function is called as follows:
*(spi->rx_buf) = read_dr(info->regs);
which the compiler, with full optimizations on, turns it into:
ld_s r2,[r1,24] <- the spi->rx_buf
sr 0x80000000,[r4] <- this is the strobe bit write !!!
lr r4,[r4] <- this is the FIFO read!!!
stb r4,[r2] <- store the result
Unfortunately, the read from the FIFO is always 0 since the FIFO data is
not yet available.
During my investigations, I found that the following code works:
sys_out32(1 << 31, info->regs + 0xd);
*(spi->rx_buf) = sys_in32(info->regs + 0xd);
This does, basically, the same thing. But the compiler inserts an
instruction in between the write/read:
sr 0x80000000,[r4] <- write of the strobe bit!!!
ld_s r2,[r1,24] <- the pointer goes to r2
lr r4,[r4] <- read from FIFO!!!
stb r4,[r2] <- store the result
A single clock cycle between writing the register and reading seems
to be enough for the data to become available for reading.
This patch adds a nop in the read_dr() inline function.
Change-Id: I0c216d5738d5771835b1052e2e83363e8e3abf0c
Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Though it's an ARC core, Quark SE SS does not follow the same registers
mapping as the official DesignWare document. Some parts are common, some
not.
Instead of bloating spi_dw.c with a lot of #ifdef or rewriting a whole
new driver though the logic is 99% the same, it's then better to:
- centralize common macros and definitions into spi_dw.h
- have a specific spi_dw_quark_se_ss_reg.h for register map, clock
gating and register helpers dedicated to Quark SE SS.
- have a spi_dw_regs.h for the common case, i.e. not Quark SE SS.
GPIO CS emulation and interrupt masking ends up then in spi_dw.h.
Clock gating is specific thus found in respective *_regs.h header.
Adding proper interrupt masks to quark_se_ss soc.h file as well.
One of the main difference is also the interrupt management: through one
line or multiple lines (one for each interrupt: rx, tx and error). On
Quark SE Sensor Sub-System it has been set to use multiple lines, thus
introducing relevant Kconfig options and managing those when configuring
the IRQs.
Quark SE SS SPI controller is also working on a lower level, i.e. it
requires a tiny bit more logic from the driver. Main example is the data
register which needs to be told what is happening from the driver.
Taking the opportunity to fix minor logic issues:
- ICR register should be cleared by reading, only on error in the ISR
handler, but it does not harm doing it anyway and because Quark SE SS
requires to clear up interrupt as soon as they have been handled,
introducing a clear_interrupts() function called at the and of the ISR
handler.
- TXFTLR should be set after each spi_transceive() since last pull_data
might set it to 0.
- Enable the clock (i.e. open the clock gate) at initialization.
- No need to mask interrupts at spi_configure() since these are already
masked at initialization and at the end of a transaction.
- Let's use BIT() macro when relevant.
Change-Id: I24344aaf8bff3390383a84436f516951c1a2d2a4
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>
Laurentiu Palcu