linux-kernel - Re: [PATCH v4 1/2] tty: hvc: pass DMA capable memory to put

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Date:   Sat, 7 Aug 2021 23:00:27 +0800
From:   Xianting Tian <xianting.tian@...ux.alibaba.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     gregkh <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, Amit Shah <amit@...nel.org>,
        Omar Sandoval <osandov@...com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE" 
        <virtualization@...ts.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH v4 1/2] tty: hvc: pass DMA capable memory to put_chars()


在 2021/8/6 下午10:51, Arnd Bergmann 写道:
> On Fri, Aug 6, 2021 at 5:01 AM Xianting Tian
> <xianting.tian@...ux.alibaba.com> wrote:
>> @@ -163,6 +155,13 @@ static void hvc_console_print(struct console *co, const char *b,
>>          if (vtermnos[index] == -1)
>>                  return;
>>
>> +       list_for_each_entry(hp, &hvc_structs, next)
>> +               if (hp->vtermno == vtermnos[index])
>> +                       break;
>> +
>> +       c = hp->c;
>> +
>> +       spin_lock_irqsave(&hp->c_lock, flags);
> The loop looks like it might race against changes to the list. It seems strange
> that the print function has to actually search for the structure here.
>
> It may be better to have yet another array for the buffer pointers next to
> the cons_ops[] and vtermnos[] arrays.
I will make the change in v5, thanks.
>
>> +/*
>> + * These sizes are most efficient for vio, because they are the
>> + * native transfer size. We could make them selectable in the
>> + * future to better deal with backends that want other buffer sizes.
>> + */
>> +#define N_OUTBUF       16
>> +#define N_INBUF                16
>> +
>> +#define __ALIGNED__ __attribute__((__aligned__(sizeof(long))))
> I think you need a higher alignment for DMA buffers, instead of sizeof(long),
> I would suggest ARCH_DMA_MINALIGN.

thanks, I will fix it in v5:

#define __ALIGNED__ __attribute__((__aligned__(ARCH_DMA_MINALIGN)))

>
>         Arnd