Hi Simon, On Thu, 2018-02-22 at 09:17 -0700, Simon Glass wrote: > Hi, > > On 21 February 2018 at 05:26, Alexey Brodkin > <alexey.brod...@synopsys.com> wrote: > > Synopsys Data Fusion subsystem (DFSS) is targeted to deeply built-in > > use-cases and so to save some silicon area decision was made to > > escape usage of any busses and use instead directly wired to CPU > > peripherals. And one of those is DW APB UART. > > > > Later DFSS became a part of larger and more complicated SoCs with > > some other peripherals connected via common buses but default UART > > is still used via ARC core's auxulary registers which are not mapped > > to "normal" address space and we use very special instructions to access > > them, thus we cannot simply reuse whatever accessor we have in 16550 > > UART as of now. > > > > Also we cannot just switch inb()/outb() to access ARC AUX regs always > > for DFSS because other peripherals have normal memory-mapped control > > registers and we need to use normal accessors for them. > > > > Frankly I don't like a lot what I did here but otherwise if I create > > a special driver for this I'll need to reimplement > > ns16550_serial_ops.putc()/getc() which will be pure copy-paseted from > > ns16550.c because the only difference is only in > > ns16550_{read|write}b(). > > > > As mentioned above we cannot remap those auxiliary registers to > > normal memory address-space and thus we have to use very special > > accessors write_aux_reg()/read_aux_reg() that directly use special > > CPU intructions (namely LR/SR) for dealing with ARC AUX regs. > > > > Also note here I just use a check for a particular SoC being selected > > (CONFIG_ARCH_DFSS will be introduced shortly) but that is done just for > > simplicity, otherwise it might be a slecial Kconfig option for NS16550 > > or anything else. > > > > I'd like to know what people think about possible colutions here. > > And as always any comments are much appreciated! > > > > Signed-off-by: Alexey Brodkin <abrod...@synopsys.com> > > Cc: Simon Glass <s...@chromium.org> > > Cc: Tom Rini <tr...@konsulko.com> > > Cc: Stefan Roese <s...@denx.de> > > --- > > drivers/serial/ns16550.c | 11 +++++++++-- > > 1 file changed, 9 insertions(+), 2 deletions(-) > > I think a separate driver might be better, unless we want to make the > read/write interface go through regmap or similar?
But in case of ARC's AUX regs portmap won't help because those AUX regs are couldn't be mapped - that a completely different address space and we may only access them via dedicated instructions (LR vs LD and SR vs ST). -Alexey _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot