From: Ahmad Fatoum <a.fatoum@pengutronix.de>
To: Tomas Marek <tomas.marek@elrest.cz>,
Sascha Hauer <s.hauer@pengutronix.de>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH 5/6] i2c: efi: avoid 64-bit division
Date: Thu, 15 Aug 2024 08:57:18 +0200 [thread overview]
Message-ID: <f8931b23-768b-429e-a634-b28494fb95fa@pengutronix.de> (raw)
In-Reply-To: <Zr2XxoD4Gce7bTB4@debian>
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@elrest.cz>
>> Signed-off-by: Ahmad Fatoum <a.fatoum@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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next prev parent reply other threads:[~2024-08-15 6:57 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-14 9:24 [PATCH 1/6] common: pe: fix use of undefined macro for ARMv7 Ahmad Fatoum
2024-08-14 9:24 ` [PATCH 2/6] efi: fs: fix determination of read-only files Ahmad Fatoum
2024-08-14 9:24 ` [PATCH 3/6] filetype: fix else clause indentation Ahmad Fatoum
2024-08-14 9:24 ` [PATCH 4/6] acpi: fix compilation for 32-bit Ahmad Fatoum
2024-08-14 9:24 ` [PATCH 5/6] i2c: efi: avoid 64-bit division Ahmad Fatoum
2024-08-15 5:53 ` Tomas Marek
2024-08-15 6:57 ` Ahmad Fatoum [this message]
2024-08-19 6:16 ` Sascha Hauer
2024-08-14 9:24 ` [PATCH 6/6] net: fsl_enetc: fix compilation for 32-bit Ahmad Fatoum
2024-08-14 11:08 ` [PATCH 1/6] common: pe: fix use of undefined macro for ARMv7 Sascha Hauer
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