dmaengine: dw-edma: Simplify debugfs context CSRs init procedure

dmaengine: dw-edma: Simplify debugfs context CSRs init procedure

DW eDMA v4.70a and older have the read and write channels context CSRs
indirectly accessible, which means CSRs like Channel Control, Xfer size,
SAR, DAR and LLP address are accessed at a fixed MMIO address, with their
reference to the corresponding channel determined by the Viewport CSR. To
have a coherent access to these registers the CSR IOs are supposed to be
protected with a spinlock. DW eDMA v4.80a and newer normally have unrolled
Read/Write channel context registers, with these CSRs directly mapped in
the controller MMIO space.

Both normal and viewport-based registers are exposed via debugfs nodes, and
the original algorithm was based on the unrolled CSRs mapping and
recalculated the viewport addresses when required. This is unscalable (it
only supports a platform with a single eDMA since a base address is
statically preserved) and also needlessly overcomplicated (it loops over
all Rd/Wr context addresses and recalculates the viewport base address on
each debugfs node access).

Simplify the algorithm by adding the channel ID and its direction fields in
the eDMA debugfs node descriptor. These new fields can be used to find a
CSR offset in the channel register space. The DW eDMA debugfs node getter
will also use them to activate the respective context CSRs viewport before
reading data from the specified register. For the unrolled CSR mapping, no
spinlock or viewport activation is needed.

Note: this replaces some REGISTER() uses with CTX_REGISTER(), which avoids
an implicit dependency on a local variable name.  The same problem with the
rest of the macro will be fixed in the next commit.

Link: https://lore.kernel.org/r/20230113171409.30470-16-Sergey.Semin@baikalelectronics.ru
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Vinod Koul <vkoul@kernel.org>