[PATCH 5/6] i2c: efi: avoid 64-bit division
Ahmad Fatoum
a.fatoum at pengutronix.de
Wed Aug 14 23:57:18 PDT 2024
Hello Tomas,
On 15.08.24 07:53, Tomas Marek wrote:
> Hello Ahmad,
>
> Thanks for maintenance of the Barebox EFI.
>
> On Wed, Aug 14, 2024 at 11:24:23AM +0200, Ahmad Fatoum wrote:
>> I2C message length is 16 bit, so doing a 64-bit division is overkill.
>> Let's remove the cast and just rely on the usual integer promotion
>> to 32-bit.
>>
>> Cc: Tomas Marek <tomas.marek at elrest.cz>
>> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
>> ---
>> drivers/i2c/busses/i2c-efi.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-efi.c b/drivers/i2c/busses/i2c-efi.c
>> index 5f6cc0eed28e..a666a28fab51 100644
>> --- a/drivers/i2c/busses/i2c-efi.c
>> +++ b/drivers/i2c/busses/i2c-efi.c
>> @@ -114,7 +114,7 @@ static unsigned int efi_i2c_msg_op_cnt(const struct efi_i2c_priv *i2c_priv,
>>
>> max_len = efi_i2c_max_len(i2c_priv, msg);
>>
>> - return ((u64)msg->len + max_len - 1) / max_len;
>> + return (msg->len + max_len - 1) / max_len;
>
> The issue here is that max_len, which represents the MaximumReceiveBytes
> or MaximumTransmitBytes in EFI I2C capabilities, is 32-bit. In some EFI
> implementations (including the one I use), the EFI I2C MaximumReceiveBytes
> and MaximumTransmitBytes are set to the maximum value (0xFFFFFFFF). This
> causes msg->len + max_len - 1 to overflow, leading to an incorrect number
> of returned operations. To address this, the msg->len is extended to 64 bits.
Thanks for the info. See the patch I just Cc'd you on.
@Sascha, can you drop this one patch again?
Thanks,
Ahmad
>
> Best regards
>
> Tomas
>
>> }
>>
>> static unsigned int efi_i2c_req_op_cnt(
>> --
>> 2.39.2
>>
>
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