Re: [PATCH v2] fpga: bridge: incorrect set to clear freeze_illegal_request register

["NG, TZE YEE" <tze.yee.ng@altera.com>]

On 28/9/2026 6:25 pm, Xu Yilun wrote:
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> 
> On Sun, Sep 20, 2026 at 07:23:51PM -0700, tze.yee.ng@altera.com wrote:
>> From: Tanmay Kathpalia <tanmay.kathpalia@altera.com>
>>
>> A Partial Region Controller can be connected to one or more
>> Freeze Bridge. Each Freeze Bridge has an illegal_request
>> bit represented in the freeze_illegal_request register.
> 
> Why only this register reveals details about multiple bridges, while
> other registers always operate on all of them? And how can we understand
> which bridges are actually in use.
> 

Hi Yilun,

The Partial Region Controller fans its single freeze signal out to all 
bridges via a Conduit Splitter, so the status (0x00) and ctrl (0x04) 
registers act on them collectively. But each bridge drives its own 
single-bit illegal_request, and a Conduit Merger concatenates these into 
the n-bit, write-1-to-clear freeze_illegal_request register (0x08), bit 
i is the bridge on freeze interface i, n = number of freeze interfaces. 
(See the Quartus Prime Pro PR User Guide, Conduit Splitter/Merger.)

The driver need not track n: the read value already identifies the 
bridges flagging an illegal request, and writing it back clears exactly 
those bits. Writing a literal 1 clears only bit 0, leaving every other 
bridge latched, so this patch fixes the bug. I'll add this to the commit 
message in v3.

>> Thus, instead of just set to clear the illegal_request bit
>> for first Freeze Bridge, we need to ensure the set to clear
> 
> Imperative mood.
> 

Will fix in v3, e.g. "Clear every illegal_request bit that is set, 
instead of clearing only the bit for the first Freeze Bridge."

Thanks,
Tze Yee

>> action is applied to which ever Freeze Bridge that has
>> occurrence of illegal request.
>>
>> Fixes: ca24a648f535 ("fpga: add altera freeze bridge support")
>> Cc: stable@vger.kernel.org # v4.10+
>>
>> Signed-off-by: Tanmay Kathpalia <tanmay.kathpalia@altera.com>
>> Signed-off-by: Tze Yee Ng <tze.yee.ng@altera.com>
>> ---
>> Taking over this patch from Tanmay.
>>
>> Changes in v2:
>> - Add "Cc: stable@vger.kernel.org # v4.10+" into the signoff area so the
>>    stable-kernel rule is satisfied (reported by kernel test robot).
>> - Remove Chiau Ee's signoff as he is no longer working on this patch.
>>
>> Link v1:
>> https://lore.kernel.org/all/20250311151601.12264-1-tanmay.kathpalia@altera.com/
>> ---
>>   drivers/fpga/altera-freeze-bridge.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/fpga/altera-freeze-bridge.c b/drivers/fpga/altera-freeze-bridge.c
>> index c24c976117c8..2591dcc53d83 100644
>> --- a/drivers/fpga/altera-freeze-bridge.c
>> +++ b/drivers/fpga/altera-freeze-bridge.c
>> @@ -51,7 +51,7 @@ static int altera_freeze_br_req_ack(struct altera_freeze_br_data *priv,
>>                if (illegal) {
>>                        dev_err(dev, "illegal request detected 0x%x", illegal);
>>
>> -                     writel(1, csr_illegal_req_addr);
>> +                     writel(illegal, csr_illegal_req_addr);
>>
>>                        illegal = readl(csr_illegal_req_addr);
>>                        if (illegal)
>> --
>> 2.43.7
>>
>>