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Subject: Re: [PATCH v4 08/18] net: davinci_emac: potentially get the MAC
 address from MTD
From:   David Lechner <david@lechnology.com>
To:     Bartosz Golaszewski <brgl@bgdev.pl>, Sekhar Nori <nsekhar@ti.com>,
        Kevin Hilman <khilman@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Grygorii Strashko <grygorii.strashko@ti.com>,
        "David S . Miller" <davem@davemloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Lukas Wunner <lukas@wunner.de>, Rob Herring <robh@kernel.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Lunn <andrew@lunn.ch>, Jonathan Corbet <corbet@lwn.net>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-omap@vger.kernel.org, netdev@vger.kernel.org,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>
References: <20180629094039.7543-1-brgl@bgdev.pl>
 <20180629094039.7543-9-brgl@bgdev.pl>
 <e2579b81-7c66-8be6-fcad-ab7a3a5b0765@lechnology.com>
Message-ID: <ee49a8de-0812-a619-25be-4c6d8a35cc81@lechnology.com>
Date:   Fri, 29 Jun 2018 15:35:27 -0500
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On 06/29/2018 03:09 PM, David Lechner wrote:
> On 06/29/2018 04:40 AM, Bartosz Golaszewski wrote:
>> From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>>
>> On da850-evm board we can read the MAC address from MTD. It's currently
>> done in the relevant board file, but we want to get rid of all the MAC
>> reading callbacks from the board file (SPI and NAND). Move the reading
>> of the MAC address from SPI to the emac driver's probe function.
>>
>> Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>> ---
>>   drivers/net/ethernet/ti/davinci_emac.c | 20 ++++++++++++++++++--
>>   1 file changed, 18 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/ti/davinci_emac.c b/drivers/net/ethernet/ti/davinci_emac.c
>> index a1a6445b5a7e..48e6a7755811 100644
>> --- a/drivers/net/ethernet/ti/davinci_emac.c
>> +++ b/drivers/net/ethernet/ti/davinci_emac.c
>> @@ -67,7 +67,7 @@
>>   #include <linux/of_irq.h>
>>   #include <linux/of_net.h>
>>   #include <linux/mfd/syscon.h>
>> -
>> +#include <linux/mtd/mtd.h>
>>   #include <asm/irq.h>
>>   #include <asm/page.h>
>> @@ -1783,7 +1783,10 @@ static int davinci_emac_probe(struct platform_device *pdev)
>>       struct cpdma_params dma_params;
>>       struct clk *emac_clk;
>>       unsigned long emac_bus_frequency;
>> -
>> +#ifdef CONFIG_MTD
>> +    size_t mac_addr_len;
>> +    struct mtd_info *mtd;
>> +#endif /* CONFIG_MTD */
>>       /* obtain emac clock from kernel */
>>       emac_clk = devm_clk_get(&pdev->dev, NULL);
>> @@ -1815,6 +1818,19 @@ static int davinci_emac_probe(struct platform_device *pdev)
>>           goto err_free_netdev;
>>       }
>> +#ifdef CONFIG_MTD
> 
> What about the case when MTD is compiled as a module?
> 
>> +    mtd = get_mtd_device_nm("MAC-Address");
> 
> What about the case when PTR_ERR(mtd) == -EPROBE_DEFER?

To answer my own question: because get_mtd_device_nm() doesn't
ever return -EPROBE_DEFER.

I'm trying to make this work on LCDK, but the emac driver probes
before any mtd device is registered, so, I just get -ENODEV even
though I've added a partition to the device tree labeled
"MAC-Address". You can see in the kernel messages that MTD is
not probed until later.

> 
>> +    if (!IS_ERR(mtd)) {
>> +        rc = mtd_read(mtd, 0, ETH_ALEN,
>> +                  &mac_addr_len, priv->mac_addr);
>> +        if (rc == 0)
>> +            dev_info(&pdev->dev,
>> +                 "Read MAC addr from SPI Flash: %pM\n",
>> +                 priv->mac_addr);
>> +        put_mtd_device(mtd);
>> +    }
>> +#endif /* CONFIG_MTD */
>> +
>>       /* MAC addr and PHY mask , RMII enable info from platform_data */
>>       memcpy(priv->mac_addr, pdata->mac_addr, ETH_ALEN);
>>       priv->phy_id = pdata->phy_id;
>>
>