Re: [PATCH] net: stmmac: use dma_addr_t for DMA addresses

On 8/12/26 2:23 AM, Maxime Chevallier wrote:
> Hi Alex,
> 
> On 8/11/26 21:27, Alex Elder wrote:
>> In jumbo_frm() (implemented in both "chain_mode.c" and "ring_mode.c"),
>> an unsigned integer local variable is used to hold the value returned
>> by dma_map_single().  On systems where a dma_addr_t is 64 bits, the
>> subsequent dma_mapping_error() check of the returned value operates
>> only on the low 32 bits (whose high bit won't be sign-extended).  In
>> this case, dma_mapping_error() would return 0 (no error) even if there
>> were one.
>>
>> Fix this in both spots by using a dma_addr_t for the local variable.
> 
> Thanks :)
> 
> I was wondering if it would silently hides another address size related
> issue a little bit lower, as we now have :
> 
>    dma_addr_t des2;
> 
>    des2 = dma_map_single(...);
> 
>    desc->des2 = cpu_to_le32(des2);
> 
> desc->des2 is __le32, so for 64 bit addresses we silently truncate the
> address.

I saw that too.  Everything is unsigned, and only the lower
32 bits will be used, but I'd rather see the dma_addr_t
explicitly converted to u32 before being passed to cpu_to_le32().
This should work regardless of the size of dma_addr_t:

	desc->des2 = cpu_to_le32(lower_32_bits(des2));

I didn't look, but there could be other places where this occurs.
Tell me if you'd like me to send another patch that does this
(here and in any other spots I find.)
> However I don't see how jumbo would work on 64-bits anyways as des3 is the next
> chunk of the jumbo frame...
> 
> I think this is good as-is, so
> 
> Reviewed-by: Maxime Chevallier <[email protected]>

Thank you.

					-Alex

> Maxime
> 
>>
>> Reported-by: Sashiko <[email protected]>
>> Link: https://lore.kernel.org/linux-devicetree/[email protected]/
>> Signed-off-by: Alex Elder <[email protected]>
>> ---
>>   drivers/net/ethernet/stmicro/stmmac/chain_mode.c | 3 ++-
>>   drivers/net/ethernet/stmicro/stmmac/ring_mode.c  | 3 ++-
>>   2 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/chain_mode.c b/drivers/net/ethernet/stmicro/stmmac/chain_mode.c
>> index fc04a23342cfc..ec25193d287bb 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/chain_mode.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/chain_mode.c
>> @@ -20,9 +20,10 @@ static int jumbo_frm(struct stmmac_tx_queue *tx_q, struct sk_buff *skb,
>>   	unsigned int nopaged_len = skb_headlen(skb);
>>   	struct stmmac_priv *priv = tx_q->priv_data;
>>   	unsigned int entry = tx_q->cur_tx;
>> -	unsigned int bmax, buf_len, des2;
>> +	unsigned int bmax, buf_len;
>>   	unsigned int i = 1, len;
>>   	struct dma_desc *desc;
>> +	dma_addr_t des2;
>>   
>>   	desc = tx_q->dma_tx + entry;
>>   
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/ring_mode.c b/drivers/net/ethernet/stmicro/stmmac/ring_mode.c
>> index 78fc6aa5bbe95..664d8cfb58cdc 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/ring_mode.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/ring_mode.c
>> @@ -20,8 +20,9 @@ static int jumbo_frm(struct stmmac_tx_queue *tx_q, struct sk_buff *skb,
>>   	unsigned int nopaged_len = skb_headlen(skb);
>>   	struct stmmac_priv *priv = tx_q->priv_data;
>>   	unsigned int entry = tx_q->cur_tx;
>> -	unsigned int bmax, len, des2;
>> +	unsigned int bmax, len;
>>   	struct dma_desc *desc;
>> +	dma_addr_t des2;
>>   
>>   	if (priv->extend_desc)
>>   		desc = (struct dma_desc *)(tx_q->dma_etx + entry);
>>
>> base-commit: 31397cf1819210bd63fa3d2c7d8c24f7c8667d99
>