Re: [PATCH 2/2] iommu/omap: Add support for configuring dsp iommus on DRA7xx

* Suman Anna [off-list ref] [150722 09:25]:

On 07/22/2015 12:26 AM, Tony Lindgren wrote:

quoted

I don't like using syscon for tinkering directly with SoC registers.

This is not a SoC-level register, but a register within a sub-module of
the DSP processor sub-system. The DSP_SYSTEM sub-module in general is
described in Section 5.3.3 of the TRM [1], and it implements different
functionalities like the PRCM handshaking, wakeup logic and DSP
subsystem top-level configuration. It is a module present within the DSP
processor sub-system, so can only be accessed when the sub-system is
clocked and the appropriate reset is released.

OK so if it's specific to the DSP driver along the lines of sysc and
syss registers.

Typically we handle these registers by mapping them to the PM runtime
functions for the interconnect so we can reset and idle the hardware
modules even if there is no driver, see for example
omap54xx_mmu_dsp_hwmod.
 

quoted

We should use some Linux generic framework for configuring these
bits to avoid nasty dependencies between various hardware modules
on the SoC.

What does DSP_SYS_MMU_CONFIG register do? It seems it's probably
a regulator or a gate clock? If so, it should be set up as a
regulator or a clock and then the omap-iommu driver can just
use regulator or clcok framework to request the resource.

No, its neither. It is a control bit that dictates whether the
processor/EDMA addresses go through the respective MMU or not. The
register currently has 4 bits (bit 0 in each nibble), one each for
enabling each MMU and requesting an MMU abort on each. The MMU
integration and enablement notes are detailed in Section 5.3.6 of the
TRM [1], and the DSP_SYS_MMU_CONFIG register layout is in Table 5-28
(Page 1641).

OK yeah seems like it should be handled by the DSP driver during
probe after doing pm_runtime_get. Then the driver can configure
things like IOMMU and load firmware. Or am I missing something here?

Regards,

Tony

 

[1] http://www.ti.com/lit/ug/spruhz6/spruhz6.pdf