On Tue, Feb 23, 2016 at 03:29:55PM +0000, Anurag Kumar Vulisha wrote: > Hi Arnd, > > > -----Original Message----- > > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > > Sent: Tuesday, February 23, 2016 3:51 PM > > To: Anurag Kumar Vulisha > > Cc: robh+dt@xxxxxxxxxx; pawel.moll@xxxxxxx; mark.rutland@xxxxxxx; > > ijc+devicetree@xxxxxxxxxxxxxx; galak@xxxxxxxxxxxxxx; tj@xxxxxxxxxx; > > devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux- > > ide@xxxxxxxxxxxxxxx; Anirudha Sarangi; Srikanth Vemula; Punnaiah Choudary > > Kalluri > > Subject: Re: [RFC PATCH] drivers: ata: Read Rx water mark value from device- > > tree > > > > On Tuesday 23 February 2016 05:58:32 Anurag Kumar Vulisha wrote: > > > > > > > > I don't know what is appropriate because I have no idea what > > > > Rxwatermark is good for. Can you try describing why we can't just > > > > set it to the correct value for everyone automatically? > > > > > > > > > > This RX watermark level sets the minimum number of free locations > > > within the RX FIFO .When the rx fifo level crosses the programmed > > > watermark level ,sata controller will transmit HOLDS to the device asking it > > to wait. This happens when dma reads the rx fifo data slower than the device > > is sending the data. Note that it can take some time for the HOLDs to get to > > the other end and in the time there must be enough room in the FIFO to > > absorb all data that could arrive from the device. > > > Currently we are using 0x40 for this value, which works fine with all > > > hardware designs we are currently having. But hoping that this value > > > may vary for future silicon versions, I wanted to make this as a configurable > > value. So for this reason I thought of moving it either to device-tree or > > making it as a module_param() property. > > > > > > > Ok, so if this depends on the silicon version, your initial approach would be > > better than the module_param. > > > > I would probably make this dependent on the compatible string instead, and > > have a table in the device driver that uses a specific value for each variant of > > the device, but either way should be fine. > > > > Having a separate property is most appropriate if for each hardware revision > > there is exactly one ideal value, while a table in the driver makes more sense > > if this takes a bit of tuning and the driver might choose to optimize it > > differently based on other constraints, such as its own interrupt handler > > implementation. > > > > Since we are currently having one value in common for all the hardware and also changing > the rx water mark does not require any changes other than vendor specific PTC register update , > I think it would be better to use device tree property for that rx watermark value. Doing > this makes the updating of rx watermark value easy, if any changes required. > > In future, if any silicon version rx water mark value doesn't work with the current versions, > then I will do as you said by maintaining the table in device driver. But at present I feel > that single rx watermark property in device tree would be enough, since it works with all the > hardware versions we have. If you currently have no reason to modify it now, then add it later when you actually have a use case. Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
