Re: [PATCH v4 1/2] tty: hvc: pass DMA capable memory to put_chars()

[Xianting TIan]

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@xxxxxxxxxxxxxxxxx> 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.
>
> > +/*
> > + * 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.

As some ARCH(eg, x86, riscv) doesn't define ARCH_DMA_MINALIG, so i think 
it 's better remain the code unchanged,

I will send v5 patch soon.

>         Arnd