linux-kernel - Re: [PATCH 4/4] ata: pata_parport: fit3: implement IDE command set registers

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Message-ID: <640e1c7a-4356-70b7-d881-df13c8d72447@kernel.org>
Date:   Thu, 5 Oct 2023 07:43:01 +0900
From:   Damien Le Moal <dlemoal@...nel.org>
To:     Ondrej Zary <linux@...y.sk>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:     Christoph Hellwig <hch@....de>,
        Sergey Shtylyov <s.shtylyov@....ru>,
        Tim Waugh <tim@...erelk.net>,
        linux-parport@...ts.infradead.org, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] ata: pata_parport: fit3: implement IDE command set
 registers

On 10/5/23 03:52, Ondrej Zary wrote:
> fit3 protocol driver does not support accessing IDE control registers
> (device control/altstatus). The DOS driver does not use these registers
> either (as observed from DOSEMU trace). But the HW seems to be capable
> of accessing these registers - I simply tried bit 3 and it works!
> 
> The control register is required to properly reset ATAPI devices or
> they will be detected only once (after a power cycle).
> 
> Tested with EXP Computer CD-865 with MC-1285B EPP cable and
> TransDisk 3000.
> 
> Signed-off-by: Ondrej Zary <linux@...y.sk>
> ---
>  drivers/ata/pata_parport/fit3.c | 16 ++++------------
>  1 file changed, 4 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/ata/pata_parport/fit3.c b/drivers/ata/pata_parport/fit3.c
> index bad7aa920cdc..86b39966755b 100644
> --- a/drivers/ata/pata_parport/fit3.c
> +++ b/drivers/ata/pata_parport/fit3.c
> @@ -9,11 +9,6 @@
>   *
>   * The TD-2000 and certain older devices use a different protocol.
>   * Try the fit2 protocol module with them.
> - *
> - * NB:  The FIT adapters do not appear to support the control
> - * registers.  So, we map ALT_STATUS to STATUS and NO-OP writes
> - * to the device control register - this means that IDE reset
> - * will not work on these devices.
>   */
>  
>  #include <linux/module.h>
> @@ -35,10 +30,11 @@
>   * cont = 1 - access the IDE command set
>   */
>  
> +static int cont_map[] = { 0x00, 0x08 };
> +
>  static void fit3_write_regr(struct pi_adapter *pi, int cont, int regr, int val)
>  {
> -	if (cont == 1)
> -		return;
> +	regr += cont_map[cont];

It is a little silly to have that cont_map array for this only... Why not simply
"regr += cont << 3;" ? Sergey suggested that already I think.

>  
>  	switch (pi->mode) {
>  	case 0:
> @@ -59,11 +55,7 @@ static int fit3_read_regr(struct pi_adapter *pi, int cont, int regr)
>  {
>  	int  a, b;
>  
> -	if (cont) {
> -		if (regr != 6)
> -			return 0xff;
> -		regr = 7;
> -	}
> +	regr += cont_map[cont];
>  
>  	switch (pi->mode) {
>  	case 0:

-- 
Damien Le Moal
Western Digital Research