linux-kernel - Re: [PATCH v2 1/1] i2c: qcom-geni: Support systems with 32MHz serial engine clock

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Message-ID: <2de5f3e7-1fd6-4368-94bc-4eecc8fc6752@quicinc.com>
Date: Sun, 29 Sep 2024 12:06:33 +0530
From: Manikanta Mylavarapu <quic_mmanikan@...cinc.com>
To: Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
        <andi.shyti@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <quic_srichara@...cinc.com>, <quic_varada@...cinc.com>
Subject: Re: [PATCH v2 1/1] i2c: qcom-geni: Support systems with 32MHz serial
 engine clock



On 9/26/2024 3:58 PM, Vladimir Zapolskiy wrote:
> Hello Manikanta.
> 
> On 9/26/24 06:43, Manikanta Mylavarapu wrote:
>> In existing socs, I2C serial engine is sourced from XO (19.2MHz).
>> Where as in IPQ5424, I2C serial engine is sourced from GPLL0 (32MHz).
>>
>> The existing map table is based on 19.2MHz. This patch incorporate
>> the clock map table to derive the SCL clock from the 32MHz source
>> clock frequency.
>>
>> Signed-off-by: Manikanta Mylavarapu <quic_mmanikan@...cinc.com>
>> ---
>> Changes in v2:
>>     - Dropped IPQ5424 from the commit title
>>     - Added else part to assign geni_i2c_clk_map_19p2mhz to itr
>>     - Dropped MHZ macro and used HZ_PER_MHZ macro
>>     - Expanded SE to serial engine
>>     - Added the reason for 32MHz clock in commit message
>>
>>   drivers/i2c/busses/i2c-qcom-geni.c | 19 ++++++++++++++++---
>>   1 file changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
>> index 212336f724a6..22f2a0d83641 100644
>> --- a/drivers/i2c/busses/i2c-qcom-geni.c
>> +++ b/drivers/i2c/busses/i2c-qcom-geni.c
>> @@ -16,6 +16,7 @@
>>   #include <linux/pm_runtime.h>
>>   #include <linux/soc/qcom/geni-se.h>
>>   #include <linux/spinlock.h>
>> +#include <linux/units.h>
>>     #define SE_I2C_TX_TRANS_LEN        0x26c
>>   #define SE_I2C_RX_TRANS_LEN        0x270
>> @@ -146,18 +147,30 @@ struct geni_i2c_clk_fld {
>>    * clk_freq_out = t / t_cycle
>>    * source_clock = 19.2 MHz
>>    */
>> -static const struct geni_i2c_clk_fld geni_i2c_clk_map[] = {
>> +static const struct geni_i2c_clk_fld geni_i2c_clk_map_19p2mhz[] = {
>>       {KHZ(100), 7, 10, 11, 26},
>>       {KHZ(400), 2,  5, 12, 24},
>>       {KHZ(1000), 1, 3,  9, 18},
>>   };
>>   +/* source_clock = 32 MHz */
>> +static const struct geni_i2c_clk_fld geni_i2c_clk_map_32mhz[] = {
>> +    {KHZ(100), 7, 14, 18, 40},
>> +    {KHZ(400), 4,  3, 11, 20},
>> +    {KHZ(1000), 4, 3,  6, 15},
>> +};
> 
> Please double check the values.
> 
> This is what I get:
> * for 100KHz: 32000000 / (40 * 7) ~ 114286, apparently 32000000 / (40 * 8) would
> be a better fit, however it's unclear what would be proper t_high / t_low values,
> * for 400KHz: it seems good,
> * for 1000KHz: 32000000 / (15 * 4) ~ 533333, which is almost 1/2 of the wanted
> bus frequency, so this one looks very wrong.
> 
> Do you have any ideas how to get better bus frequency settings?
> 

Thanks for pointing this out.

I will double check and get back with the proper data.

Thanks & Regards,
Manikanta.