On 05/24/2012 03:03 PM, Thierry Reding wrote:
- Stephen Warren wrote:
On 05/24/2012 01:03 AM, Thierry Reding wrote:
Upon reset, the CRC_OSC_CTRL register defaults to a 13 MHz oscillator input frequency. With Lucas' recent commit b8cb519 ("tegra2: trivially enable 13 mhz crystal frequency) applied, this breaks on hardware that provides a different frequency.
Can you expand upon "breaks"? Do you mean "detects the wrong value", or "causes U-Boot to fail to execute successfully", or...
For reference, I have this commit in my local branch, and have run U-Boot on at least a couple of our boards without any apparent issue.
But, I agree there is a problem that should be fixed; I'm just not sure what the current impact is.
On Tamonten, U-Boot doesn't execute properly. Or at least I can't tell because it may just be that there is no output whatsoever on the serial port (perhaps due to the peripheral clock being configured wrongly?).
Strange thing is that if I don't do the frequency detection and without Lucas' patch things still work, even though CRC_OSC_CTRL contains the value for a 13 MHz clock.
Have you tested on Harmony? I believe that has a 12 MHz oscillator as well, so it should have the same problem than Tamonten.
Odd. Yes, I have tested on Harmony. I think all/most of the boards I have use a 12MHz clock.
I wonder if this is due to some incorrect setting in your BCT?
- /* + * Configure oscillator frequency. If the measured
frequency isn't + * among those supported, keep the default and hope for the best. + */ + if (frequency >= CLOCK_OSC_FREQ_COUNT) { + value = readl(&clkrst->crc_osc_ctrl); + value &= ~OSC_FREQ_MASK; + value |= frequency << OSC_FREQ_SHIFT; + writel(value, &clkrst->crc_osc_ctrl); + } +}
The above is quite different from what the kernel does, which is the following:
static unsigned long tegra2_clk_m_autodetect_rate(struct clk *c) { u32 auto_clock_control = clk_readl(OSC_CTRL) & ~OSC_CTRL_OSC_FREQ_MASK;
c->rate = clk_measure_input_freq(); switch (c->rate) { case 12000000: auto_clock_control |= OSC_CTRL_OSC_FREQ_12MHZ; break; case 13000000: auto_clock_control |= OSC_CTRL_OSC_FREQ_13MHZ; break; case 19200000: auto_clock_control |= OSC_CTRL_OSC_FREQ_19_2MHZ; break; case 26000000: auto_clock_control |= OSC_CTRL_OSC_FREQ_26MHZ; break; default: pr_err("%s: Unexpected clock rate %ld", __func__, c->rate); BUG(); } clk_writel(auto_clock_control, OSC_CTRL); return c->rate; }
Is there a specific reason for U-Boot not to do the same thing here?
I can't see any difference between the two. Except that the U-Boot code doesn't BUG(), but instead continues hoping for the best.
The kernel code supports 4 explicit rates, and if the measured clock is any of those rates, it writes the appropriate enum to the OSC_CTRL register.
However, the U-Boot code above only writes to OSC_CTRL in the case where no known match was found. Perhaps it's just that:
- if (frequency >= CLOCK_OSC_FREQ_COUNT) {
should be:
- if (frequency < CLOCK_OSC_FREQ_COUNT) {
Given that though, I'm confused why this patch makes any difference, unless I'm just totally misreading it?
I think when I first read your patch, I thought there were other differences between kernel and U-Boot, but upon further inspection I think not.