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Message-ID: <92699f07-0efc-e471-d886-c7d6c83f352e@opensource.wdc.com>
Date:   Tue, 29 Mar 2022 17:15:12 +0900
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Subject: Re: [PATCH 01/21] dt-bindings: ata: sata: Extend number of SATA ports
Content-Language: en-US
To:     Serge Semin <Sergey.Semin@baikalelectronics.ru>,
        Hans de Goede <hdegoede@redhat.com>,
        Jens Axboe <axboe@kernel.dk>, Rob Herring <robh+dt@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>
Cc:     Serge Semin <fancer.lancer@gmail.com>,
        Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@baikalelectronics.ru>,
        linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org
References: <20220324001628.13028-1-Sergey.Semin@baikalelectronics.ru>
 <20220324001628.13028-2-Sergey.Semin@baikalelectronics.ru>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <20220324001628.13028-2-Sergey.Semin@baikalelectronics.ru>
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On 3/24/22 09:16, Serge Semin wrote:
> The denoted in the description upper limit only concerns the Port
> Multipliers, but not the actual SATA ports. It's an external device
> attached to a SATA port in order to access more than one SATA-drive. So
> when it's attached to a SATA port it just extends the port capability
> while the number of actual SATA ports stays the same. For instance on AHCI
> controllers the number of actual ports is determined by the CAP.NP field
> and the PI (Ports Implemented) register. AFAICS in general the maximum
> number of SATA ports depends on the particular controller implementation.
> Generic AHCI controller can't have more than 32 ports (since CAP.NP is of
> 5 bits wide and PI register is 32-bits size), while DWC AHCI SATA
> controller can't be configured with more than 8 ports activated. So let's
> discard the SATA ports reg-property restrictions and just make sure that
> it consists of a single reg-item.
> 
> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> ---
>  Documentation/devicetree/bindings/ata/sata-common.yaml | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/ata/sata-common.yaml b/Documentation/devicetree/bindings/ata/sata-common.yaml
> index 7ac77b1c5850..c619f0ae72fb 100644
> --- a/Documentation/devicetree/bindings/ata/sata-common.yaml
> +++ b/Documentation/devicetree/bindings/ata/sata-common.yaml
> @@ -41,11 +41,10 @@ patternProperties:
>      properties:
>        reg:
>          minimum: 0
> -        maximum: 14

Why remove this ? Since AHCI can have up to 32 ports, then change the
value to 31. As the comment at the top of the file says, this is not
intended to be a device tree binding spec, but defines properties common
to most adapters.

>          description:
> -          The ID number of the drive port SATA can potentially use a port
> -          multiplier making it possible to connect up to 15 disks to a single
> -          SATA port.
> +          The ID number of the SATA port. Aside with being directly used
> +          each port can have a Port Multiplier attached thus allowing to
> +          access more than one drive by means of a single channel.

Please add a comma after "Aside with being directly used", otherwise the
sentence is hard to understand. And replace "channel" with "SATA port" to
stick with the terms defined here.

>  
>  additionalProperties: true
>  


-- 
Damien Le Moal
Western Digital Research