linux-kernel - Re: [PATCH v2] stmmac: CSR clock configuration fix

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Date:   Fri, 23 Dec 2016 09:09:17 +0800
From:   Phil Reid <preid@...ctromag.com.au>
To:     Joao Pinto <Joao.Pinto@...opsys.com>, peppe.cavallaro@...com,
        davem@...emloft.net, seraphin.bonnaffe@...com
Cc:     hock.leong.kweh@...el.com, niklas.cassel@...s.com, pavel@....cz,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2] stmmac: CSR clock configuration fix

G'day Joao,
On 23/12/2016 01:06, Joao Pinto wrote:
> Às 4:57 PM de 12/22/2016, Phil Reid escreveu:
>> On 22/12/2016 23:47, Joao Pinto wrote:
>>>
>>> Hello Phil,
>>>
>>> Às 3:42 PM de 12/22/2016, Phil Reid escreveu:
>>>> G'day Joao,
>>>>
>>>> On 22/12/2016 20:38, Joao Pinto wrote:
>>>>> When testing stmmac with my QoS reference design I checked a problem in the
>>>>> CSR clock configuration that was impossibilitating the phy discovery, since
>>>>> every read operation returned 0x0000ffff. This patch fixes the issue.
>>>>>
>>>>> Signed-off-by: Joao Pinto <jpinto@...opsys.com>
>>>>> ---
>>>>> changes v1->v2 (David Miller)
>>>>> - DWMAC100 and DWMAC1000 csr clocks masks should also be fixed for the patch
>>>>> to make sense
>>>>>
>>>>>  drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c | 2 +-
>>>>>  drivers/net/ethernet/stmicro/stmmac/dwmac100_core.c  | 2 +-
>>>>>  drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c    | 8 ++++----
>>>>>  3 files changed, 6 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c
>>>>> b/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c
>>>>> index b21d03f..94223c8 100644
>>>>> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c
>>>>> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c
>>>>> @@ -539,7 +539,7 @@ struct mac_device_info *dwmac1000_setup(void __iomem
>>>>> *ioaddr, int mcbins,
>>>>>      mac->mii.reg_shift = 6;
>>>>>      mac->mii.reg_mask = 0x000007C0;
>>>>>      mac->mii.clk_csr_shift = 2;
>>>>> -    mac->mii.clk_csr_mask = 0xF;
>>>>> +    mac->mii.clk_csr_mask = GENMASK(4, 2);
>>>>
>>>> Should this not be GENMASK(5,2)
>>>
>>> According to Universal MAC databook (valid for MAC100 and MAC1000), we have:
>>>
>>> Bits: 4:2
>>> 000 60-100 MHz clk_csr_i/42
>>> 001 100-150 MHz clk_csr_i/62
>>> 010 20-35 MHz clk_csr_i/16
>>> 011 35-60 MHz clk_csr_i/26
>>> 100 150-250 MHz clk_csr_i/102
>>> 101 250-300 MHz clk_csr_i/124
>>> 110, 111 Reserved
>>>
>>> So only bits 2, 3 and 4 should be masked.
>>>
>>> Thanks.
>>>
>> But this is a change in behaviour from what was there isn't.
>> Previous mask was 4 bits. now it's 3.
>>
>> And for example the altera socfgpa implementation in the cyclone V has valid values
>> for values 0x8-0xf, using bit 5:2.
>
> According to the databook, bit 5 is reserved and RO. When reserved, it is
> possible to customize. Is that the case? If there is hardware using the 5th bit
> we can put it GENMASK(5, 2) with no problem.
>
I've also checked the Aria 10 documentation and bit 5 is also RW.
The following options are documented and supported
     1000: CSR clock/4
     1001: CSR clock/6
     1010: CSR clock/8
     1011: CSR clock/10
     1100: CSR clock/12
     1101: CSR clock/14
     1110: CSR clock/16
     1111: CSR clock/18
They do mention that these values will probably be outside the IEEE 802.3 specified range.

But there's at least a couple of cores out there where GENMASK(5,2) is valid.
Can't say if anyone is using that setting thou.


-- 
Regards
Phil Reid