2015-05-19 13:18 GMT+02:00 Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>:
> Hi Alan,
>
>
> 2015-05-19 18:48 GMT+09:00 One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx>:
>>> I intentionally use deeper indentation for *_SHIFT
>>> because I want to clearly show UNIPHIER_UART_LCR_SHIFT
>>> belongs to UNIPHIER_UART_LCR_MCR register.
>>
>> Seems sensible to do it that way to me and a lot of other bits of the
>> kernel do.
>>
>> The only other question I have is about the unipher_serial_out. If I am
>> writing a "special" register then the sequence becomes
>>
>> - read 32bits
>> - modify
>> - write 32bits
>>
>> That means that it's no longer atomic safe as the kernel expects.
>> Checking the users FCR seems safe, LCR is probably safe and MCR likewise
>> so I don't see a problem but I think it's worth noting in case anyone
>> else does.
>
> Uh, I missed this.
> I am a bit afraid what if LCR and MCR are updated at the same time.
>
> Is it better to add mutex for writing special case registers?
>
> if (normal) {
> writel(value, p->membase + offset);
> } else {
> /* special case: two registers share the same address. */
> u32 tmp = readl(p->membase + offset);
> struct uniphier8250_priv *priv = p->private_data;
>
> mutex_lock(&priv->atomic_write_lock);
> tmp &= ~(0xff << valshift);
> tmp |= value << valshift;
> writel(tmp, p->membase + offset);
> mutex_unlock(&priv->atomic_write_lock);
> }
>
>
> If it is OK, I can fix it in v4.
>
>
>
>
>> Finally can you add a comment in serial_in and serial_out where one
>> switch case drops through into the next so its obvious to anyone looking
>> at Coverity and other analyser output that this drop through was
>> intentional ?
>
> I thought about it, too.
>
> My previous version was as follows:
>
>
> +#define UNIPHIER_UART_CHAR_FCR 3
> +#define UNIPHIER_UART_CHAR_SHIFT 8 /* Character Register */
> +#define UNIPHIER_UART_FCR_SHIFT 0 /* FIFO Control Register */
> +#define UNIPHIER_UART_LCR_MCR 4
> +#define UNIPHIER_UART_LCR_SHIFT 8 /* Line Control Register */
> +#define UNIPHIER_UART_MCR_SHIFT 0 /* Modem Control Register */
> +#define UNIPHIER_UART_DLR 9 /* Divisor Latch Register */
>
> [snip]
>
> +static void uniphier_serial_out(struct uart_port *p, int offset, int value)
> +{
> + int valshift = 0;
> + bool normal = false;
> +
> + switch (offset) {
> + case UART_FCR:
> + offset = UNIPHIER_UART_CHAR_FCR;
> + valshift = UNIPHIER_UART_FCR_SHIFT;
> + break;
> + case UART_LCR:
> + offset = UNIPHIER_UART_LCR_MCR;
> + valshift = UNIPHIER_UART_LCR_SHIFT;
> + /* Divisor latch access bit does not exist. */
> + value &= ~(UART_LCR_DLAB << valshift);
> + break;
> + case UART_MCR:
> + offset = UNIPHIER_UART_LCR_MCR;
> + valshift = UNIPHIER_UART_MCR_SHIFT;
> + break;
> + default:
> + normal = true;
> + break;
> + }
>
>
>
> I thought it was clear to anyone although it was a bit redundant and
> Matthias was opposed to it.
>
> I personally prefer clear code to tricky code that requires comments.
Me too :)
What I wanted to say was, that in the case statement you don't need to
set valshift to zero as this is the default value when entering
uniphier_serial_out. This way you can get rid of
UNIPHIER_UART_MCR_SHIFT and UNIPHIER_UART_FCR_SHIFT.
Sorry, I didn't explained myself.
Cheers,
Matthias
--
motzblog.wordpress.com
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