linux-kernel - Re: [PATCH] spi: dw: Fix wrong FIFO level setting for long xfers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHp75Vc3+_SiVFzmJPM2dtPqUGErGY6Qc6_deS1yaDkjtT35rQ@mail.gmail.com>
Date:   Fri, 13 Jan 2023 19:33:16 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Sergey Nazarov <Sergey.Nazarov@...kalelectronics.ru>,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi: dw: Fix wrong FIFO level setting for long xfers

On Fri, Jan 13, 2023 at 6:57 PM Serge Semin
<Sergey.Semin@...kalelectronics.ru> wrote:
>
> Due to using the u16 type in the min_t() macros the SPI transfer length
> will be cast to word before participating in the conditional statement
> implied by the macro. Thus if the transfer length is greater than 64KB the
> Tx/Rx FIFO threshold level value will be determined by the leftover of the
> truncated after the type-case length. In the worst case it will cause
> having the "Tx FIFO Empty" or "Rx FIFO Full" interrupts triggered on each
> word sent/received to/from the bus. In its turn it will cause the
> dramatical performance drop.
>
> The problem can be easily fixed by using the min() macros instead of
> min_t() which doesn't imply any type casting thus preventing the possible
> data loss.

But this would be problematic if the types of the parameters are different.
Currently they are u32 vs. unsigned int. I would rather assume that
FIFO length is always less than or equal to 64K and just change the
type in min_t to follow what dws->tx_len is.

-- 
With Best Regards,
Andy Shevchenko