Hi Stefan,
On 12/31/2016 12:07 AM, Stefan Herbrechtsmeier wrote:
Hi,
[snip]
In Conclusion, host's maximum value is used. ("max_frequency" property is used to QUIRK_BROKEN_CAP_CLOCK_BASE in Linux kernel.)
The conclusion is wrong. The host->max_clk isn't influenced by the max-frequency. The mmc drivers supplies the host->max_clk via the get_max_clock function if QUIRK_BROKEN_CAP_CLOCK_BASE is set. The mmc->f_max is equal to host->max_clk or max-frequency if set. This means you only need max-frequency if it is lower than the host->max_clk.
My comments refer to the linux kernel sdhci implementation.
I knew it's referred to Linux kernel.
host->max_clk is influenced by max-frequency.
Where is the host->max_clk influenced by the max-frequency?
get_max_clock function? where is get_max_clock() function used?
It is used in the kernel to set host->max_clk if the SDHCI_QUIRK_CAP_CLOCK_BASE_BROKEN is set.
Your patches didn't apply yet. waiting for Michal's review.
Only one patch is waiting Michal's review and the mmc clock separation could be applied without the other patches.
Yep, If there are no issue, i will pick the patch relevant to MMC. My meaning isn't "your patch is wrong". Your patch is right way. but if u-boot didn't implement everything like kernel, I'm believing that current u-boot is changing to status likes Linux kernel
Did you know what means the quirk for broken clock base? It means host->max_clk can be 0 or other.
It means that the host->max_clk could not be extracted from the SDHCI_CAPABILITIES and need to be provided by the driver.
Then it should be lower than min_clk likes your mentions. To prevent this, getting from max_frequency property.
Why do you think that max-frequency influences the host->max_clk? The host->max_clk could be read from the SDHCI_CAPABILITIES or need to be provided by the driver. The host->max_clk is a fixed clock rate and the mmc->f_max limits the generated frequencies of the sdhci controller. The host->max_clk depends on the processor and the mmc->f_max depends on the board, card and so on.
The host->max_clk is used for the calculation of the divider and multiplier. It represents the clock rate of the controller. The mmc->f_max limits the clock rate of the card.
Yes, mmc->f_max is card's maximum frequency. You can see how to control the clock in drivers/mmc/mmc.c
Kernel and u-boot have to check the card and host's clock values. And needs to choose the one of them.. f_max is not getting from card. Also it's assigned from host controller.
The mmc->f_max and host->max_clk have different purposes. The mmc->f_max limits the requested frequency. The host->max_clk represents the clock frequency in front of the divider and optional multiplier and is used to calculate the divider and multiplier. The host->max_clk depends on the CMU and is never changed. The mmc->f_max depends on the board.
Really ideal approach is "Using the clk_set_rate()/clk_get_rate() from CMU"..but some controllers don't fully support yet the CMU.
You only need the clk_get_rate() to get the host->max_clk or let the driver set this value as my patch does.
No. we needs to have both "clk_get_rate() and clk_set_rate()".
Of_course, it needs to consider the base clock broken case.
The whole discussion is about the base clock broken case. Otherwise the host->max_clk is extracted from the SDHCI_CAPABILITIES. The linux kernel use a callback to request the host->max_clk from the driver in the base clock broken case. The current u-boot implementation only supports the host->max_clk but call it unfortunately mmc->cfg->f_max which could be mistaken as mmc->f_max from the kernel which represents max-frequency.
Linux kernel has two options. One is get_max_clock(), the other is "using 'max-frequency' property".
Kever's patch is not problem.
The problem is that the patch "init the clock rate to max-frequency" and this is wrong and differs from the kernel which use the assigned-clock-rates. What happens if somebody sets the max-frequency to 400000? Does the clock controller supports such a low frequency? What happens if the clock controller use a different clock as requested and the mmc framework assume the requested clock rate?
Agreed this point, It needs to implement the clk_set_rate() in rockchip_sdhci.c. with value passed by set_ios().
Does we speak about the sdhci or dw_mmc controller? The sdhci don't change the host->max_clk and don't need the clk_set_rate(). It have its own divider and optional multiplier and doesn't change the base clock.
sdhci and dwmmc controller are using the clk_set_rate() in each SoC's drivers. Since driver's divider has a limitation. So i think it needs to use the "clk_set_rate()".
The mmc drivers shouldn't use the max-frequency to request a clock rate. It should only request the current clock rate or set a default clock rate independent of the max-frequency.
Back to this patch. It should use the CONFIG_ROCKCHIP_SDHCI_MAX_FREQ in the clk_set_rate() or use the default rate and only request it with clk_get_rate().
Maybe my last patch could be generalized and the max-frequency support could be moved inside the sdhci driver.
I don't want to use CONFIG_ROCKCHIP_SDHCI_MAX_FREQ...i will remove the all CONFIG_xxxx for using value.
Best Regards, Jaehoon Chung
Regards Stefan