Hi Brian,
On 15-10-06 06:41 AM, Brian Norris wrote:
Is there a reason not to do this reset unconditionally? I recall this came up in
discussion previously, when the OpenWRT folks were trying to integrate with
BCMA, where this reset was one of the few differences between the platform-
device-based driver (i.e., this one) and the BCMA based driver. Might it help
simplify things a bit if we just did the same thing everywhere?
This driver is currently shared by Cygnus and NS2.
We had similar suggestion when this patch was reviewed
internally in Broadcom.
The rationale for adding optional DT flag is as follows:
1. The NAND controller reset is currently required for NS2 only so
that it is in sane state before any NAND commands are issued. We
are not sure if Cygnus and all future iProc SoCs will require NAND
controller reset.
I'm not sure this is a very strong reason. It seems fairly reasonable in
general to reset a HW block before using it.
Efficient Boot time is a very strong reason for needing this actually.
We use the NAND controller in the bootROM, boot1/BL1, u-boot/UEFI, and
then Kernel stage. By properly initializing the controller once we do
not need to reset it 4 different times.
2. The NAND controller reset in probe would certainly increase
Linux boot time so for certain iProc SoCs we might choose avoid
NAND controller reset to reduce boot time if possible.
I recall this reason being mentioned before. I believe this only happens
because the brcmnand driver doesn't yet handle configuring the timing
registers, so iProc is implicitly relying on the bootloader to configure
the NAND timings. Perhaps it's time that we fix that. I'd rather not add
extra DT properties unless we actually need to [1]. And having proper
timing configuration in the Linux driver will help improve speeds for
all users (whose timings may not be configured in the bootloader).
This is the very reason we need the optional reset property. We need to
have timings configured by the linux driver or not. Yes, in some cases
we will be relying on earlier boot stages to configure some of the hardware.
I actually had some preliminary work to do some timing configuration
according to the new timing information from nand_base.c/nand_timing.c.
Unfortunately, I didn't complete this, and I'm no longer working at
Broadcom, so I don't exactly have access to the HW docs for all the NAND
controller revisions, nor do I have access to as much HW for testing...
Brian
[1] If we really do need a device tree differentiation, perhaps it would
be better to just differentiate the compatible string than to have
individual boolean properties. e.g.:
compatible = "brcm,iproc-nand-ns2", ...;
As described above - the option is not SoC specific. It is system
specific. In some systems we may wish to reset the NAND controller in
linux. In some we may wish to rely on initialization that has already
been done to speed up boot times.
Regards,
Scott
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