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Subject[RFC PATCH v2 4/5] mtd: rawnand: gpmi: validate controller clock rate
Date
What to do when the real rate of the gpmi clock is not equal to the
required one? The solutions proposed in [1] did not lead to a conclusion
on how to validate the clock rate, so, inspired by the document [2], I
consider the rate correct only if not lower or equal to the rate of the
previous edo mode. In fact, in chapter 4.16.2 (NV-DDR) of the document [2],
it is written that "If the host selects timing mode n, then its clock
period shall be faster than the clock period of timing mode n-1 and
slower than or equal to the clock period of timing mode n.". I thought
that it could therefore also be used in this case, without therefore
having to define the valid rate ranges empirically.

For example, suppose that gpmi_nfc_compute_timings() is called for edo
mode 5 configuration (100MHz, from the `edo_modes' table) but the rate
returned by clk_round_rate() is 80MHz (edo mode 4 from the `edo_modes'
table). In this case gpmi_nfc_compute_timings() will return error, and
will be called again for edo mode 4 configuration, which this time will
be successful.

[1] https://lore.kernel.org/r/20210702065350.209646-5-ebiggers@kernel.org
[2] http://www.onfi.org/-/media/client/onfi/specs/onfi_3_0_gold.pdf?la=en

Co-developed-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>

---

Changes in v2:
- Fix commit description.
- Add an example to the commit description to better understand the
problem solved by the patch.
- Split the patch.

drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c | 24 ++++++++++++++++++----
1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
index 4ac695aa5131..7ae7a37775a3 100644
--- a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
+++ b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
@@ -665,8 +665,8 @@ static const struct edo_mode edo_modes[] = {
* RDN_DELAY = ----------------------- {3}
* RP
*/
-static void gpmi_nfc_compute_timings(struct gpmi_nand_data *this,
- const struct nand_sdr_timings *sdr)
+static int gpmi_nfc_compute_timings(struct gpmi_nand_data *this,
+ const struct nand_sdr_timings *sdr)
{
struct gpmi_nfc_hardware_timing *hw = &this->hw;
struct resources *r = &this->resources;
@@ -679,6 +679,7 @@ static void gpmi_nfc_compute_timings(struct gpmi_nand_data *this,
u16 busy_timeout_cycles;
u8 wrn_dly_sel;
int i, emode = ARRAY_SIZE(edo_modes) - 1;
+ long clk_rate;

/* Search the required EDO mode */
for (i = 0; i < ARRAY_SIZE(edo_modes); i++) {
@@ -688,7 +689,18 @@ static void gpmi_nfc_compute_timings(struct gpmi_nand_data *this,
}
}

- hw->clk_rate = clk_round_rate(r->clock[0], edo_modes[emode].clk_rate);
+ clk_rate = clk_round_rate(r->clock[0], edo_modes[emode].clk_rate);
+ if (emode > 0 && !(clk_rate <= edo_modes[emode].clk_rate &&
+ clk_rate > edo_modes[emode - 1].clk_rate)) {
+ dev_err(this->dev,
+ "edo mode %d clock setting: expected %ld, got %ld\n",
+ emode, edo_modes[emode].clk_rate, clk_rate);
+ return -ENOTSUPP;
+ }
+
+ dev_dbg(this->dev, "edo mode %d @ %ld Hz\n", emode, clk_rate);
+
+ hw->clk_rate = clk_rate;
wrn_dly_sel = edo_modes[emode].wrn_dly_sel;

/* SDR core timings are given in picoseconds */
@@ -731,6 +743,7 @@ static void gpmi_nfc_compute_timings(struct gpmi_nand_data *this,
hw->ctrl1n |= BF_GPMI_CTRL1_RDN_DELAY(sample_delay_factor) |
BM_GPMI_CTRL1_DLL_ENABLE |
(use_half_period ? BM_GPMI_CTRL1_HALF_PERIOD : 0);
+ return 0;
}

static int gpmi_nfc_apply_timings(struct gpmi_nand_data *this)
@@ -786,6 +799,7 @@ static int gpmi_setup_interface(struct nand_chip *chip, int chipnr,
{
struct gpmi_nand_data *this = nand_get_controller_data(chip);
const struct nand_sdr_timings *sdr;
+ int ret;

/* Retrieve required NAND timings */
sdr = nand_get_sdr_timings(conf);
@@ -801,7 +815,9 @@ static int gpmi_setup_interface(struct nand_chip *chip, int chipnr,
return 0;

/* Do the actual derivation of the controller timings */
- gpmi_nfc_compute_timings(this, sdr);
+ ret = gpmi_nfc_compute_timings(this, sdr);
+ if (ret)
+ return ret;

this->hw.must_apply_timings = true;

--
2.32.0
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