Samsung/S3C6410/Mini6410: how to handle NAND's "clock off"

On Wednesday 12 November 2014 10:14:58 Uwe Kleine-K?nig wrote:

Hello again,

[extending audience a bit]

On Tue, Nov 11, 2014 at 07:42:26PM +0100, Uwe Kleine-K?nig wrote:

quoted

On Tue, Nov 11, 2014 at 07:10:33PM +0100, Juergen Borleis wrote:

quoted

Hi,

the S3C2410 NAND driver [1] can still be used for NANDs attached to an
S3C6410 SoC. But this driver has a "nice" feature called "clock off" to
save some power while not in use. I tried it here on my Mini6410
platform and it freezes the system.

The clock tree is somehow:

[...]
  hclk                      4            4   133000000          0 0
     hclk_mfc               0            0   133000000          0 0
     hclk_mem0              2            2   133000000          0 0
        mem0_srom           0            0   133000000          0 0
        mem0_nfcon          1            1   133000000          0 0
        mem0_onenand0       0            0   133000000          0 0
        mem0_onenand1       0            0   133000000          0 0
        mem0_cfcon          0            0   133000000          0 0
[...]

On the Mini6410 the "mem0_nfcon" clock is the only single user of the
"hclk_mem0". And this clock is required to keep the access to the
external network device enabled. When the NAND driver disables its
clock "mem0_nfcon", the "hclk_mem0" gets also disabled because there is
no consumer anymore. The next time the network driver tries to access
its device, the SoC freezes.

Sounds like the network driver should hold a reference to hclk_mem0.

After talking to J?rgen by phone, the solution that the dm9000 driver
should handle the clock sounds wrong. The clk in question is needed by
the SoC to operate the bus the dm9000 is connected to. So I think the
right approach would include

I think we need the same here for the S3C6410 SoC, like the imx-weim driver is 
for i.MX SoCs.

jbe

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