[PATCH v4 2/2] mtd: rawnand: meson: add support for Amlogic NAND flash controller

Hello Martin,

On 9/22/2018 11:32 PM, Martin Blumenstingl wrote:

Hello,

On Thu, Sep 20, 2018 at 10:51 AM Jianxin Pan [off-list ref] wrote:
[snip]

quoted

+static int meson_nfc_clk_init(struct meson_nfc *nfc)
+{
+       int ret;
+
+       /* request core clock */
+       nfc->core_clk = devm_clk_get(nfc->dev, "core");
+       if (IS_ERR(nfc->core_clk)) {
+               dev_err(nfc->dev, "failed to get core clk\n");
+               return PTR_ERR(nfc->core_clk);
+       }
+
+       nfc->device_clk = devm_clk_get(nfc->dev, "device");
+       if (IS_ERR(nfc->device_clk)) {
+               dev_err(nfc->dev, "failed to get device clk\n");
+               return PTR_ERR(nfc->device_clk);
+       }
+
+       nfc->phase_tx = devm_clk_get(nfc->dev, "tx");
+       if (IS_ERR(nfc->phase_tx)) {
+               dev_err(nfc->dev, "failed to get tx clk\n");
+               return PTR_ERR(nfc->phase_tx);
+       }
+
+       nfc->phase_rx = devm_clk_get(nfc->dev, "rx");
+       if (IS_ERR(nfc->phase_rx)) {
+               dev_err(nfc->dev, "failed to get rx clk\n");
+               return PTR_ERR(nfc->phase_rx);
+       }

neither the "rx" nor the "tx" clock are documented in the dt-bindings patch

ok, i will add them later.

quoted

+       /* init SD_EMMC_CLOCK to sane defaults w/min clock rate */
+       regmap_update_bits(nfc->reg_clk, 0,
+                          CLK_SELECT_NAND | CLK_ALWAYS_ON | CLK_DIV_MASK,
+                          CLK_SELECT_NAND | CLK_ALWAYS_ON | CLK_DIV_MASK);

clk_set_rate also works for clocks that are not enabled yet (except if
they have the flag CLK_SET_RATE_UNGATE)
this should help you to remove CLK_DIV_MASK here

if not set clk_div_mask here, the value 0x00 of divider means nand clock 
off, even read/write nand register is forbidden.

is CLK_SELECT_NAND a bit that switches the clock output from the sdmmc
controller to the NAND controller?
if so: can this be modeled as a mux clock?

it seems to like a gate. 1: nand is selected; 0: emmc is selected.
Is it suitable for making it as a mux clock?

the public S905 datasheet doesn't mention CLK_ALWAYS_ON at bit 28 but
uses bit 24 instead. the description from the datasheet:
Cfg_always_on:
1: Keep clock always on
0: Clock on/off controlled by activities.
     Any APB3 access or descriptor execution will turn clock on.
Recommended value: 0

can you please explain what CLK_ALWAYS_ON does and why it has to be 1?

em , it is the same as bit 24 in S905 datasheet, only moves to bit 28.
it means keeping internal clock on whether nand wroks or not.
it doesn't have to be 1; i have tried 0 successfully on AXG platform.

Regards
Martin

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