Hi Tomasz,
On Mon, Jun 3, 2013 at 8:55 PM, Tomasz Figa t.figa@samsung.com wrote:
Hi Yadwinder,
On Thursday 30 of May 2013 12:25:40 Yadwinder Singh Brar wrote:
Hi Doug,
On Thu, May 30, 2013 at 5:14 AM, Doug Anderson dianders@chromium.org
wrote:
Vikas / Yadwinder,
On Wed, May 29, 2013 at 6:37 AM, Vikas Sajjan vikas.sajjan@linaro.org
wrote:
From: Yadwinder Singh Brar yadi.brar@samsung.com
This patch defines a common rate_table which will contain recommended p, m, s, k values for supported rates that needs to be changed for changing corresponding PLL's rate.
Signed-off-by: Yadwinder Singh Brar yadi.brar@samsung.com
drivers/clk/samsung/clk-exynos4.c | 8 ++++---- drivers/clk/samsung/clk-exynos5250.c | 14 +++++++------- drivers/clk/samsung/clk-pll.c | 14 ++++++++++++-- drivers/clk/samsung/clk-pll.h | 33 +++++++++++++++++++++++++++++++-- 4 files changed, 54 insertions(+), 15 deletions(-)
I also reviewed this in our gerrit https://gerrit.chromium.org/gerrit/#/c/56742/, but I'll summarize here for the list...
struct clk * __init samsung_clk_register_pll35xx(const char *name,
const char *pname, const void __iomem *base)
const char *pname, const void __iomem *base,const struct samsung_pll_rate_table *rate_table,const unsigned int rate_count)Feels like you should document here that rate_table needs to be sorted and the sort order.
sure, we will add comment to sort the table in descending order.
+struct samsung_pll_rate_table {
unsigned int rate;nit: extra space before "int" should be removed.
ok
Also: you can include rate here if you need a convenient place to store it (which sadly means that this structure can't be const). ...but I do like Tomasz's idea of actually calculating it. You can't know it at compile time since the parent rate comes from the device tree.
compatible = "samsung,clock-xxti"; clock-frequency = <24000000>;
Actually this table should contain the recommended values and if we see the user manual, the input(parent) rate is also a part of recommended table of different output rate for a particular PLL for that SoC.
From what I understood in the documentation is that there is a set of recommended P, M, S (, K) tuples for each PLL and they are not dependent on input frequency - f_in and f_out are provided in the table just for reference to see the relation between output frequency and input frequency.
If input rate(f_in) gets changed for PLL, then the corresponding output rates(f_out) will change by using same(common) set of recommended P, M, S (, K), and the new set of output rates(f_out) may not be the _required_ set of target rates. So we need different set of P, M, S (,K) values for different f_in.
Table should contain set of P, M, S (,K) values for the _required_ target(f_out) rates for a particular input(f_in) rate.
I think we should ask some H/W engineer about that to make sure and choose the proper implementation, which will work properly for future cases, instead of ending with something that works just with current cases.
We already asked hardware engineer about PMS values for PLL, and we got a table containing recommended P, M ,S values for a given f_in(24 MHz) and required f_out rates.
Please let me know, why you think we are specific to current cases only ?
Regards, Yadwinder
Best regards,
Tomasz Figa Linux Kernel Developer Samsung R&D Institute Poland Samsung Electronics
So as Tomasz said input(parent) rate may change with board, then, do those corresponding recommended p, m, s, k will be valid?
In case, input(parent) rate changes then we may need different set of p, m ,s, k values recommended for new input rate to get required(recommended to use) output rate.
So, we think its better that the p, m, s and k along with the parent is known at the compile time ( or DT ?), as these p, m, s, k values are very much coupled with the parent rate to achieve the required(recommended to use) output rate.
Also, since the sorted table is required (sorted based on "rate"), its better to have the rate in a const rate table.
And the whole set of recommended values should come from same place(DT or static table), to keep the things simple and consistent.
Moreover, practically for a particular SoC , we use the recommended input(parent) rate only for a PLL. So we should keep the things simple here presently.
unsigned int pdiv;unsigned int mdiv;unsigned int sdiv;unsigned int kdiv;I think kdiv is signed.
No, as these values should be the recommended values to be written in corresponding register bits. So it should remain unsigned.
K value should be considered as negative only while recalculating rate.
As per exynos5250 user manual's section 7.3.2 : " K value description "Postive value (Negative value)": Postive values is that you should write EPLLCON/VPLLCON register. Negative value is that you can calculate PLL output frequency with it."
-Doug
Regards, Yadwinder & Vikas. -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html